First: Don't just limit yourselves to what I'm interested in, there's plenty of value in discussing the other stuff.
Moving on:
Oh man, I totally forgot chromehounds. That is definitely going to have to go on the list.
Another game to throw in there people might be interested in: Battlezone: Rise of the Black Dogs.
While strictly speaking a tank game, rather than a mech game, you can still build or still mechs in most in most of the later levels. And climbing out of your tank, pulling out a sniper, shooting the pilot of a mech and then riding over to commandeer it is quite fun. Not the best mech game, but good.
As to realistic/not realist, I know mechs are inherently unrealistic, but as an example: hands. Hands ruin it for me. Who would put hands on a mech? That is just the most retarded thing, and I just can't get over it. Call it a flaw in my neural wiring, but it's all the more jarring in an otherwise fairly down-to-earth game like mechwarrior. Battletech, its fine. The whole setting is absurd, so it fits right in.
A light, thing limbed scout mech moving quickly I can buy. I know, technically unfeasable, but there's no instant mental recoil, no immediate immersion breakage that I can't shake.
- Also, was there really a starsiege 2? I loved the hell out of Starsiege. O_O
On the Mechwarrior/ Battletech thing - I was definitely not thinking Battletech here. Bluh, can't remember the name of what I'm getting it confused with. Something... fuck, it's gone. Had mechs that could turn into planes and back, mostly kicking the shit out of mechs that couldn't.