For 'older' Mechwarrior titles i would suggest:
Mechwarrior 2: Mercenaries
Fantastic campaign (Detailed contracts with contract duration period, it's kinda cool that if you make one choice you could potentially miss another due to that duration).
Amazing mech selection:
Reload and Repair feature (realistic expenses)
Graphics are actually not that bad
Jumpjets that are actually jumpjets
AMAZING soundtrack (Jeehun Hwang is awesome)
Only bugs i can think of are if you fire LRMs out of a Mad Dog's ST it'll probably hit your center... and that autocannons can be a little glitchy at some times and not do any damage (Uncommon).
MGs are also super deadly up close, if you build a 12 MG Mad Dog it'll shred 100 tonner's CT in seconds (joke build, but it works).
This is if i had to pick just one game from Mechwarrior's past, 3 is equally fun but more buggy especially now.