The Super Robot Wars series is awesome. I'm not talking about the SRTaisen OG for GBA(although it is from the same series and a good game in it's own right) I'm talking about the ones from Japan. The only ones in English are the two GBA games I just mentioned and fan-translated SRW 3 for the SNES. Its a good game, but not as user friendly as the later games. The series follows the same idea as Super Smash Brothers and Kingdom Hearts but precedes them by at least 10 years and instead of Mario you get gundam.
The early games don't have a whole bunch in plot except to give you a reason to beat up the main bad guy, but it gets better as the series has gone on. The series in the games are small in the early games consisting of the main Gundams(0079 to F91) and Super Robots mainly from Mazinger and Getter robo. The list expands to include others such as Aura battler Dunbine, Heavy Metal L-Gaim, Gundam Wing, and even G Gundam in a few of the games.
The games are SRPGs. The main units are essentially divided into Super Robots(High armor, low mobility) such as Mazingers, Getters, Gunbuster, and Evangelion and real robots(High mobility, lower armor) which I pretty much listed. I wont list all the series since theres a huge number. The games start off easily enough with you being able to kill all the units no problem. Eventually though, depending on the actions you take and how you upgrade your units, the games can vary in difficulty from challenging to murderous. Not only will bosses have ten times the health of any of your units, some can regenerate a good portion of their health and if the game hates you, can absorb attacks and heal themselves.
Here are a few videos. First is of Alpha Gaiden, a game not too difficult(okay it can get difficult) but its not too hard that you can't beat it.
http://www.youtube.com/watch?v=y8qL9SLQMMY
Next are a few of my favorite units. If these are in a game, they will be the best ones you can get.
http://www.youtube.com/watch?v=4nESGoU64oA
http://www.youtube.com/watch?v=F5NirUWJ_uU&feature=related
http://www.youtube.com/watch?v=wG1COvx55KI
And heres an example of a boss battle in Alpha 2.
http://www.crunchyroll.com/media-150191/Super-Robot-Wars-Alpha-2-Londo-Bell-vs-Nightingale.html?hires=1