I bought Scott Pilgrim vs. The World and played through it last night and I actually enjoyed it a lot more than I thought I would in single player. It is VERY slow initially. The walk speed is stupidly slow when you start, and it only ever feels "right" after you max out the stat, and even then it could stand to be a bit faster. Because of the problem with the walk speed, you're reliant on dash to get around, which is where I assume the complaints of clunkiness stem from, and while you can move along the x-axis speedily with dash, your options are more limited across the z-axis with only walk or side-step, neither of which feel particularly natural at the start of the game. There's an option to set the analog stick to immediately dash/side-step (d-pad is still double tap), and that helps slightly.
However, the fighting has some nice variety to it for such a simplistic beat-'em-up, allowing you to do some pretty neat stuff with the combo system, even in the single player. Enemies can be easily juggled, so you can pop them up in the air, dash forward and continue the combo, or if you're holding a weapon, you can toss it to bounce them and dash forward can continue from there. Your options expand a bit more once you start leveling up and earning new moves, especially with the counter that opens up fairly early. It keeps the fighting entertaining enough to last through the entire campaign AND immediate repeated playings, which I think is something of a rarity for side-scrolling BEU's.