I've seen like 1-2 episodes of G1. It's fine, obviously you can tell how old it is from the animation and designs, but I don't think it's bad.
G1.5 or G2, I haven't seen any episodes of.
I actually kinda like G3. I don't love it like i do with G4 and G5 but it's good, i like the animations and the characters are cute. I haven't seen much of it though.
I haven't seen G3.5 but from what I've seen it doesn't look like something i'd like.
Edit: I've seen all of G3 now (the original one, not the weird reboot with the baby face models). I like it, it's really cute. Aside from maybe the last 3 videos, they feel kinda out of place, and I don't know why they suddenly decided to change Rainbow Dash's voice, and remake Cheerilee's design. The intro song slaps tho