I think the only other situation I liked alternative style mechs (where there was actually variety) was the Armored Core series. I used to freaking love it. Mixing leg and body types, different arms and heads.
Was amazing. So much lost potential when they didn't continue it correctly.
The PS2 AC games were great. Spent so much time playing AC3.
Gundam Breaker is great for that kind of customization too, though it's a little simpler.
Really hope they're going to do a third game. It could be sooo good with a little more variety in the available kits and missions. Adding some of the equipment sets that are sold seperate from mobile suit kits would be nice too.