Well, I don't think 'Worlds Collide' had that much build-up either. Each crossover only alluded to the bigger plot in the last issues before the event. 'Worlds Collide' had Eggman telling Metal Sonic to meet his 'new partner' (SU#50), and 'Ivo'/'Albert' leaving their bases to activate the Genesis Wave, while their foes were busy (STH#247 & MM#23). 'Worlds Unite' has Eggman going to find the Lost Hex (STH#272), Silver ending up in X's world and Orbot being possessed by Sigma (SU#75), while Dr. Wily gets abducted by Sigma (MM#49) and Sticks encounters X (SB#7/8). Both crossovers open up with a basic "how did this all begin" montage-of-sorts, but I will admit that 'Worlds Unite' has FAR more exposition than 'Worlds Collide' did, most definitely because more franchises (Sonic Boom and Mega Man X) are involved now.
Actually, this makes me really glad that they DIDN'T bring the other worlds in for the whole story, or we'd most likely STILL be getting nothing but exposition over halfway into the crossover. I think the heroes getting along quickly is just to stop things repeating too much from the last crossover. Also, there was an explanation for the Robot Masters and Maverick Hunters getting controlled, AND there was even a small amount of foreshadowing too. It's explained in Part 1 that the Deadly Six can control machines, and that their new armour enhances that power, allowing them to even control Sigma's body (before his failsafe activates). However, they can't control the robots' minds, hence why Mega Man and X apologised to Sonic in Part 6, and Sigma still gloated to them in Part 1. As for the art, I kind of agree with you.
The problem is, none of these artists (or at least, Dan Schoening and Edwin Huang) have drawn for the Sonic OR Mega Man series. However, Dan has drawn for the IDW 'Ghostbusters' series and worked on human characters (which is why I don't mind his art-style for the human/Mega Man characters in Act 1) and Edwin Huang is an artist for UDON's Street Fighter series (which makes sense, since Act 2 will introduce that world to the crossover). Also, we at least (kinda) got some Tracy Yardley artwork during Act 1, and Tyson Hesse (who's done some covers for Sonic) is doing Act 3, so hopefully things'll get better in that regard. If not... I'll be disappointed.