From: Mr Crispy | #011
The Endless Frontier games while tangentially related to the OG games are kinda sorta more of a spinoff of Namco x Capcom (What with having the NxC original characters plus KOS-MOS and T-ELOS as well as a somewhat similar battle system).
Only OG1 and 2, and Endless Frontier 1 have been released officially in english. Only other games that have been translated are 1, 3, J, and one of the Alpha games.
this covers some of the basic/early games:
http://hardcoregaming101.net/superrobotwars/superrobotwars.htm
In terms of general continuity/plotline/subseries I believe there's:
original continuity (2-F Final as covered in that article)
Lord of Elemental (which got remade for the DS and PSP and I think got a sequel on PSP)
Alpha (1-3 and Alpha Gaiden)
OG (OG1 and 2, OGs remake, OG Gaiden, Endless Frontier 1 and 2, and the new game that hasn't come out yet)
Z (Z1, Z2 parts 1 and 2)
and many of the remaining games are kinda one-offs I think.
If you're looking at series composition, the older games are probably more heavily slanted towards older Gundams, Shin Getter, and Mazinger, while the DS and Z games have a lot more recent series or others that would be familiar to contemporary western anime fans such as Rebuild of Evangelion, Linebarrels of Iron, Voltron, Eureka Seven, Big O, Code Geass, Gurren Lagann, Aquarion, Macross Frontier, etc..
The OG games obviously do not have any anime licenses and instead seem to attempt to cram literally every original plot point/faction/character/mech from previous games into a single game. So it's naturally a bit of a mess.
Though you should take what I say with a grain of salt since I'm not really a fan, and in fact hate the series which I would put on the same level or lower as IF games. Not to mention SRW has left me incredibly bitter and jaded against the entire mecha genre as a whole.
What's IF? And why the bitter hate against the series?
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Long live Saint Seiya!!