Since people keep asking here are the major differences in SF2 compared to the SF1 series.
New items included by Thirdwire in the Strike Fighters 2 Series (As of Jan 2012)
General changes
Original 3D Aircraft look to have been reworked/replaced and have higher resolution skins
Original 3D cockpits look to have been reworked/replaced with more functionality (working dials, switches. panel lights) and higher resolution skins.
Terrains have higher resolution tiles.
The Games support Direct X 10 advanced shaders if you have a DX10 capable graphics card and Win 7 / Vista.
Better support for multicore CPUs.
Vector RHAW scope and functionality added with radar frequency ranges.
TEWS RWR with radar frequency ranges for 1978 Jets.
New file structure to make modding and patching far easier.
New Menu/hangar screens.
Screenshots save as smaller JPEGs by default.
Ability to merge all the SF2 games.
Ability to save a mission you have just flown.
"Request For Help" radio feature now works from June 2010
From Expansion 1 Bump maps can be added to skins
Revised Campaign selection screen.
Support for Force Feedback (Dec 2009).
In game Mission Editor (Expansion Pack 2 or DLC)
Radar On/Off command works(June 2011)
F12 cinematic view works - also after crashes(June 2011)
Year specific loadouts allowed in loadout.ini (July 2011)
In game options for downloads and Online Manual (May 2011)
AI terrain following improved
DLC Support added in Patches.
LAU-42 rack added for AIM-4s
Twin AIM-9 rails added
Aircraft made easier to spin on Hard FM (Jun 2010).
Radar on/off radio command now works
Attack my target Radio command added to command element (May 2011)
Ejection sequence camera view changed(May 2011)
Tree Fade added (May 2011).
Installer reworked so games can be installed and merged in any order (May 2011)
No guns option added when only left with Sidewinders in flight (Aug 2011).
Multiple Carriers now launch flights in SF2V Campaigns.
Aircraft Hangar screen can now change with skin selected
Games can check online for the latest version and be updated from within the game.[May 2011]
Blast damage to a target now counts to a players score.
Pilot pictures can now be JPGs
Rocket and Fuel pod combined armament (July 2011).
Bombers less armoured against Missile hits (Nov 2011)
Campaign Customiser DLC for SF2 released (Sep 2011)
Carrier Starts in generated Single missions (Mar 2012 SF2NA)
Multiple Ship launched SAMs and GunFire(Mar 2012 SF2NA)
Fleet name and ship lists shown on Planning map (Mar 2012 SF2NA)
AWACs name shown on Planning map (Mar 2012 SF2NA)
new DX10 only Terrain engine - 3D ground objects with collision (Mar 2012 SF2NA)
F-14 Avionics allow 6 targets to be simultaneously fired on in TWS mode (Mar 2012 SF2NA)
Carriers now populated with random Aircraft (Mar 2012 SF2NA)
New menu music (Mar 2012 SF2NA)
New voice and calls for E-2C AWACS controller (Mar 2012 SF2NA)
AI bombers can now launch Cruise Missiles from long range (Mar 2012 SF2NA)
Expansion Packs can be installed over any game at May 2013 patch or later
NEW Objects in the SF2 series ( That's in addition to the original Aircraft from the first series)
Note: A lot of the new aircraft versions have their own 3D cockpits and 3D models specific to the version - there are too many differences to note so you will just have to have fun finding them.
Strike Fighters 2
A-4B (65)
A-4C (65)
A-4E (65)
A-4E (67)
A-4F (74)
F-4B (65)
F-4B (67)
F-4C (67)
F-4D (67)
F-4D (75)
F-4E (72) - Slatted with longer gun muzzle
F-4E (75)
F-100D (64) - new model and new unique 1964 cockpit
F-100D (68) - new model and new unique 1968 cockpit
Hawker Hunter F.4 - model and skins (No Pit)
Hawker Hunter F.5 - model and skins (No Pit)
Hawker Hunter F.6 - model and skins (No Pit)
Hawker Hunter F.9 - model and skins (No Pit)
Hawker Hunter F.59 - model and skins (No Pit)
Hawker Hunter F.70 (No Pit)
Hawker Hunter F.73 (No Pit)
MiG-17 - (No Pit)
MiG-17PF - Has radar (No Pit)
J-6 - (No Pit)
MiG-21M - (No Pit)
MiG-21FL - (No Pit)
MiG-21PF - (No Pit)
MiG-21PFV - (No Pit)
MiG-21S - (No Pit)
MiG-21SM - (No Pit)
MiG-23BN - (No Pit)
MiG-23MF - (No Pit)
MiG-23MS - (No Pit)
Mirage 5D- (No Pit)
Su-7BMK - (No Pit)
Tu-16 - (No Pit)
Ground Objects
SA-2E
SA-6
ECM Pods
AN/ALQ-71
AN/ALQ-101
AN/ALQ-119
Strike Fighters 2: Vietnam
A-1H - new model and skins (No Pit)
A-1J - new model and skins (No Pit)
A-6A (No Pit)
A-7B (71)
A-7C (71)
A-7C - new A-7C model
A-7D - new A-7D model and new unique cockpit
A-7E - new A-7E model and new unique cockpit
F-100D (64) - new model and new unique 1964 cockpit
F-100D (68) - new model and new unique 1968 cockpit
F-105D(66)
F-4B(65)
F-4B(67)
F-4C(67)
F-4D(67)
F-4E(72) - slatted with longer gun muzzle
F-8C
F-8C(66)
F-8D
F-8D(66)
F-8E(66)
F-8H
F-8H(69)
F-8J
F-8J(69)
J-6 - (No Pit)
MiG-17PF - (No Pit)
Ground Objects
SA-2C
SA-2E
ECM Pods
AN/ALQ-71
AN/ALQ-101
AN/ALQ-119
Strike Fighters 2: Europe
A-7D - new A-7D model and new cockpit
A-7D(75)
A-7D (78)
A-10A(78) - New model with Pave Penny
CF-104 - New skins - (No Pit)
CF-104(72) - New skins - (No Pit)
CF-104(76) - New skins - (No Pit)
F-4C(67)
F-4D(67)
F-4D(75)
F-4D(78)
F-4E(72)
F-4E(75)
F-4E(78)
F-4F(80)
F-4M(75)
F-84F - (No Pit)
Hawker Hunter F.4 - (No Pit)
Hawker Hunter F.5 - (No Pit)
Hawker Hunter F.6
Hawker Hunter F.51 - (No Pit)
MiG-17PF - (No Pit)
MiG-21M - (No Pit)
MiG-21Bis - (No Pit)
MiG-21S - (No Pit)
MiG-21SM - (No Pit)
MiG-23BN - (No Pit)
MiG-23MF- (No Pit)
MiG-23ML- (No Pit)
MiG-23MLA - (No Pit)
MiG-23MLD - (No Pit)
Mirage 3C - (No Pit)
Mirage5F- (No Pit)
MystereIVA - (No Pit)
Su-7B - (No Pit)
Su-7BMK - (No Pit)
Super Mystere B2 - (No Pit)
Ground Objects
SA-8
SA-8B
SA-2C
SA-2E
ECM Pods
AN/ALQ-71
AN/ALQ-101
AN/ALQ-119
Strike Fighters 2:Israel
A-4H (68)
A-4H (70)
F-4E(72)
F-4E Kurnass(73)
F-4E Kurnass(75)
F-4E Kurnass(78)
Hawker Hunter F.6 - (No Pit)
Hawker Hunter F.9 - (No Pit)
Kfir C1
Kfir C1(77)
MiG-17PF - (No Pit)
MiG-21BisB - (No Pit)
MiG-21M- (No Pit)
MIG-21FL - (No Pit)
MiG-23ML - (No Pit)
MiG-23MLD - (No Pit)
Shahak (71) - (New 3D model with correct engine)
Ground Objects
Centurion8
Centurion10
Centurion13
M48A3
M60A1
ECM Pods
AN/ALQ-71
AN/ALQ-101
AN/ALQ-119
Strike Fighters 2:Israel - Expansion Pack 1
C-47A - (No Pit)
Meteor F.8
MiG-15bis - (No Pit)
P-51D
Spitfire mk 9c - (No Pit)
Spitfire mk 9e - (No Pit)
Vampire F.5 - (No Pit)
Vampire F9 - (No Pit)
Vampire F.52 - (No Pit)
MystereIVA - New cockpit
F-16A - Corrected 3D model(Should also appear in June 2010 SF2I patch)
Ground Objects
M50_Sherman
M51_Sherman
T34-85
Strike Fighters 2:Europe - Expansion Pack 2
English Electric Lightning F.1
English Electric Lightning F.1A
English Electric Lightning F.2
English Electric Lightning F.2A
English Electric Lightning F.3
English Electric Lightning F.6
English Electric Lightning F.53 (if you have SF2 merged)
Hawker Hunter F.1
Hawker Hunter F.2
Hawker Hunter F.4
NAA F-100A Super Sabre
NAA F-100A Super Sabre (58)
NAA F-100C Super Sabre
NAA F-100C Super Sabre (65)
English Electric Canberra B.2 (No pit)
English Electric Canberra B.6 (No pit)
English Electric Canberra B.20 (No pit - If you have SF2 Merged)
Yak-23 (No pit)
New Skins for C-47 and Spitfires (No pit - If you have Expansion Pack 1 Merged)
MiG-15(No pit)
Weapons
Redtop A-A Missile
Firestreak A-A Missile
Lightning Gun Pack
Strike Fighters 2:North Atlantic
Grumman F-14A Tomcat
Grumman F-14A_77 Tomcat
Vought A-7E_74 Corsair II
Grumman A-6E Intruder (No Pit)
Grumman A-6E_79 Intruder (No Pit)
Grumman E-2C Hawkeye (No Pit)
Grumman EA-6B Prowler (No Pit)
Tu-16K-10-26 Badger C (No Pit)
Tu-16K-26 Badger G (No Pit)
Tu-16K-26_73 Badger G (No Pit)
Tu-16P Badger J (No Pit)
Tu-16P_72 Badger J (No Pit)
Tu-16RM-1 Badger D (No Pit)
Tu-22KD Blinder B (No Pit)
Tu-22M2 Backfire B (No Pit)
Tu-22M3 Backfire C (No Pit)
Tu-22PD Blinder E (No Pit)
Tu-22RD Blinder C (No Pit)
Tu-95RT Bear D (No Pit)
Yak-38 Forger A (No Pit)
Ground Objects
CGN-36 California class Cruiser
CVN-68 Nimitz Class Aircraft Carrier
Gearing FRAM IB class Destroyer
Kashin class Destroyer
Kiev class Aircraft Carrier
Knox class Frigate
Krivak I class Frigate
Krivak II class Frigate
LCC-19 Blue Ridge class Amphibious Command Ship
LHA-1 Tarawa class Amphibious Assault Ship
LPD-4 Austin class Amphibious Transport Dock
Oliver Hazard Perry class Frigate
Oliver Hazard Perry (82) class Frigate
Spruance class Destroyer
Spruance (82) class Destroyer
Weapons
AIM-54A Phoenix
SA-N-3 Goblet (M-11 Shtorm) SAM
SA-N-1B Goa SAM
SA-N-4 Gecko SAM
RIM-2F Terrier SAM
RIM-7E/H Sea Sparrow SAM
RIM-66B Standard SAM
K10S (AS-2 Kipper) Cruise Missile
KH22 (AS-4 Kitchen) Cruise Missile
KSR5 (AS-6 Kingfish) Cruise Missile
Items in SF1 series removed from SF2
A-6A Cockpit in SF2V (DIANE not possible)
AV-8A in SF2E
Multiplayer (All)
O-1E Birddog (All)
FAC over CAS(All)
C-130 Hercules
F-104 cockpit