After being disappointed with Sonic 4 Episode I, a return to Sonic's 2D roots that featured some ugly art design and a brutal phsyics engine, I wasn't expecting much from Episode II. Surprisingly though, I ended up having quite a bit of fun with the sequel. The physics engine is upgraded considerably and, while still not perfect, now feels much closer to the Genesis-era games. The hideous cel-shaded character design from the first episode was also ditched in favor of a cleaner look. Level design and boss battles are also improved from Episode I. The newly-introduced "Tag Actions" feel fresh and make for some nice platforming sequences as well. On the downside, the soundtrack is hit-or-miss (mostly miss) and a little more zone variety would've been nice.
While still not on the level of the the 2D Sonic games from the Genesis days, Sonic 4 Episode II manages to hold its own and provide an enjoyable experience that retains that classic Sonic feel while tossing in a few fresh twists here and there. Worth playing if you're a fan of the series.