I'm new to collecting, starting around last October, so I can only comment on my experiences thus far. I also can't comment on the third party figures, since I can't afford any of them, but I will say they look

-ing amazing!
Having grown up with G1, I gotta say I miss metal toys. When Beast Wars first came out, their ball socket joints really blew me away; but I didn't care as much for animals turning into robots (though I loved the show). So, when I walked through the toy aisle of Target and first laid eyes on Generations Kup, I was floored. A re-envisioning of a classic character, but with ridiculous amounts of articulation? While the movies were out, halfway raping some of the concepts that made Transformers great? I immediately bought it, and I've been snatching up Classics, Generations, and RTS figures since.
The movie figures I am not impressed with. At all. I skipped all of the RID and AEC figures because I didn't like their chunky parts, where I felt a lot more transformations could be done to lower the figure's profile. (I completely missed the Universe line, which is why I will have to pay through the nose for a Universe Prime.) The movie toys went the opposite direction, at times getting way too detailed. Someone mentioned a "scrunched tin foil" look to the faces, and I completely agree. I do own a couple though, and particularly enjoy DOTM Crankcase, for his more insect-like appearance.
Design wise, I say "it depends on the series". Engineering wise, I say "hot damn!" I am more and more impressed with the transformation sequences with each figure I buy. I can't decide if Generations Red Alert or TFP Arcee is my favorite so far. Tracks is a bit wobbly, but an exception. The universal fist pegs and C-clips are ingenious, too.
A side-note on designs... I'm sick to death of seeing Bumblebee. I have a Pretenders Bumblebee and an RTS Bumblebee, and it looks like I'll stick with those for a long time.
TFP Arcee, by the way, is the only TFP figure I have. After reading that they first came out last November, I wondered why I hadn't seen any others, until I then read about the distribution issues. That's an unfortunate thing, but it doesn't surprise me too terribly much since there are still several metric tons of movie figures taking up space in stores. There may be more to it than that, but that's how it seems to me.
I'd like to know of a new series in the works, something grandiose to replace the movie figures. But I'll just have to be patient on that.
So overall, I said "good". The designs, generally speaking, are fantastic, the engineering even more so. The pricing is fair. I think once Hasbro frees itself from the typically static designs that come with movie license tie-ins, I have a good feeling we'll be seeing a lot more fun stuff in the future.