My biggest issue with the MP line is the scale. They're too fucking small now.
The original MP's up to 09 were massive; they felt like they were intended as a centerpiece of your collection (except Megs, he was crap).
Then we got MP10 Optimus, which was "more accurate" but not really, but the main problem is that he only came up to the shoulder of MP1. Mine has been in truck mode for the last 9 years. Then we get to Prowl/Wheeljack/Bublebee territory, and the figs are laughably small. Sure, they look decent, sure the engineering is fairly impressive (aside from 50% of their mass forming a backpack), but they're just unimpressive, and unimposing.
Then, let's look at price. My MP1 is the 20th Anniversary Hasbro one, cost me 100 bucks. Worth every fucking penny; the thing was an absolute marvel when released. MP10 was the TRU release for $125. I haven't seen MP44 for under $600.
I'm sure as shit not spending $200+ on a Bumblebee that's only 5 inches fucking tall.