So far, after having played it for 18 hours, the only complaint I have is the loading times. I can tolerate loading screens when switching between islands, but having them before and after battles is grating. Such transitions should be over within a second, but here it takes three to five seconds.
Other than that, it's a return to form by foregoing to put too much emphasis on a gimmick. The fourth and fifth game in the series were pleasantly long, but at the same time had repeated stretches of not so good gameplay. Brothership is more like the first and third game, but with the length of the 3DS titles (actually, it's going to be longer than them) and better structured sidequests. Features that seem to have problems in the first few hours are solved eventually, so it's smooth sailing aside from the loading times.
The new battle feature provides a lot of good options, so its inclusion works. The only negative thing I can mention here is that it takes a bit too much time until it gets unlocked during the story. The same holds true for partner attacks, so for the first five hours or so, it's all about using plain jump and hammer attacks.
The new development team has been faithful to the series and doesn't make AlphaDreams feel missed. One feature that was dropped is the stat boost reel at each level up that all previous five games had. I don't miss it, because I was quite good at it and could roll the highest numbers pretty consistently, so eventually the reels on all stats showed only one 2 and otherwise 1s, making the feature more annoying than rewarding. In Brothership you can pick permanent boosts to certain stats that trigger at each level up and that's good enough to improve your desired stats; also more reliable.
Legend11 correctly predicted that GTA IV will outsell Super Smash Bros. Brawl. I was wrong.