A lot of that engineering came from Beast Wars, including the "heads that mimic the alt mode" (re: Beast Wars Neo). Car Robot was basically, "let's take Beast Wars engineering and give them licensed vehicle modes." And it did work quite well.

I also really liked how they all had sculpted Autobot insignias in robot mode that were concealed (to various extents) in vehicle mode. It really helped to make them more like robots in disguise!

But I didn't like how Hasbro
undid this on their RiD toys by slapping Autobot logos on the vehicle modes (and then having the audacity to name the line "Robots In Disguise")
IMO the engineering of the larger figures has become a bit dated now. Super Fire Convoy and God Fire Convoy are somewhat unstable and ungainly in their combined form, and Fire Convoy suffers from chrome that chips too easily.

The carded figures on the other hand are still really good even by today's standards.

Speedbreaker and Wild Ride's asymmetrical robot forms may not be everyone's cube of Energon, but they are both good solid toys.
Gigatron's not really that great, but that's what happens when you try to shove 6 modes into a single toy... then retool it for an additional 10 modes for Devil Gigatron. Jack of all trades, master of none.
From photos that I've seen, the TF Go! gestalts really don't look as nice as Car Robot's. JMO.
I love the SpyChangers!

And here's why:
1) Whereas the larger Autobots had insignias that would be hidden in vehicle mode, they couldn't do this with the more simplistic engineering of the Spy Changers -- so instead they added Autobot logos
embedded in the paint and it's
heat sensitive! 
e.g. if you look at Ox (Ironhide), here's no Autobot logo visible, but if you put your finger on one of the sides and press it, the heat from your finger activates the Autobot logo! It's a lot like the old rub signs from G1, only that they're NOT stickers. It's like some sort of heat sensitive tampograph but coloured to perfectly blend with the paint job! That's gotta be one of the coolest gimmicks ever devised for Transformers, and it's a shame that they've never tried it again!
2) SpyChangers are
FUN to play with! Remember that these are repaints of 1995's G2 GoBots, and they were designed to be compatible with Hot Wheels and Matchbox playsets! The SpyChangers all have free-spinning axles that conserve momentum allowing the vehicle to roll for a jolly long time. You can shoot them out of launchers and onto tracks etc. Heck, a good flick with your finger will send a Spy Changer
flying across any flat surface!

When Spy Changers transform and roll out, they
seriously roll out! It is such a simple but incredibly effective gimmick. Sure, it means that the legs don't separate and they end up with large chests, but that's because the chest and legs house the free-spinning axles which need to remain inseparable in order to work. For a bunch of small cheap toys, they pack a LOT of awesomely fun play value!

Their robot modes are better designed than previous toys with free spinning axles such as the Battlechargers and Throttlebots, and even then it was only their rear axles that were free spinning (and motorised). By having both the front and rear axles spin freely, the Spy Changers can conserve greater momentum and achieve long distances
without the need of motorisation.
Yeah, I skipped Black Convoy too. Not really actively looking to get him though... if I happen to come across one cheap I'll get it, otherwise ... meh. It sucked how RiD Scourge never got released here though.
