I actually picked the pair up last week, and am having an absurd amount of fun with them!
True they are somewhat more simplistic in design, but they transform rather solidly. I give the advantage to Prime though. His biggest failing is his hollow trailer hitch area in vehicle mode, which looks awful with the exposed arms from above. Wish there were some folding panels or something to hide that. That's the biggest obstacle to overcome: making your peace with that design decision.
But once you do, you realize he looks great from the front and side, and transforms into a sturdy, surprisingly detailed robot mode depiction of the character. I like this toy better than Prime RID voy Prime in many ways. He looks more detailed and more show accurate, albeit somewhat bulky. And yes, people having been complaining about the big back pack, but it doesn't bother me. It's there and it's big, but it pegs together solidly and doesn't come undone. It doesn't get in the way of anything. And thanks to sturdy back heels, it actually doesn't affect his balance or make him back heavy. And not just the back pack, but everything just pegs together firmly and solidly. I really, really love it.
Bumblebee I like but he isn't quite as good. He doesn't come together quite as solidly as Prime does, and veers a bit more into shell former territory. Plus getting into vehicle mode, you do have set aside a minute or so to get all his vehicle mode panels into place and carefully massage them together until his car mode looks right. more trouble than prime, but that's often a problem with TF figures and Bumblebee is far from the worst case of it. Bumblebee's back pack is smaller, and still doesn't get in the way, but it's more visually obtrusive, and doesn't peg in as solidly as prime's. Still fairly sturdy though. And again, well balanced.
Yeah, they are quite different from the big, ultra detailed and complex movie leaders, but I like them. I like that they are fifteen dollars cheaper too.