I'll have to echo what everyone else said about
Alien Spidy. It just doesn't work. I think the main problem is that the game's core mechanic (rope-swinging) is one that we associate with games like Worms where mostly it's a fun and simple way to move around and doesn't require an enormous amount of precision, but the game itself is basically a torture platformer like Super Meat Boy. Everything on the screen kills you except for the exact path you need to take through the level. It feels even more linear because that path is also filled to the brim with useless pick-em-ups, which also affect your score, so actually even if you do exactly what they want but you're a few pixels off, you are punished. It's a platformer with powerups, but the powerups don't function as powerups, they function as part of the level design. Because you get them right when you need them, you use them exactly once to clear an obstacle, and then they disappear. What's the difference between the springboard mushroom and the super jump powerup? Nothing. What does the buoyancy powerup (not shown in the demo, but in videos) do? Lets you land on water once without drowing--how is that different from having a small island in the middle of the water? It's about time attack and score attack but there are no shortcuts and the only way to boost your score is to collect more and die less, not actually do anything materially different about how you move. The framerate is also iffy.
Pity, because the character is cute and I think the art style is nice and economical.
Yeah, played the demo of Alien Spidy and you completely miss any of the tutorials because you're pressing A to jump. They just disappear instantly. How do you not pick up on that?
The crazy thing is that most of the buttons on the controller don't do anything, so there's really no reason why this would be the case.
Other demos...
Shoot Many Robots: This seemed to be a pretty looking bore to me. It's a side-scrolling action shooter like Contra or Metal Slug, but with a loot system. Kill a gazillion robots, get bolts to buy better equipment. The demo was very pretty and everything, but did nothing to convince me that there'd be a variety of scenarios, enemies, or possible character builds. And unlike Contra or Metal Slug, the level design wasn't very engaging. Ho hum.
Serious Sam 3: Things I liked: fast movement speed, satisfying gory monster kills, stats menu was interesting, technically seemed to run well and look good on 360. Things I didn't like: shooting boring stationary humans, auto-aim up the wazoo, guns in demo had no real pop although the size of the gun menu was inspiring, washed out Assassin's Creed I style middle eastern urban cityscape level design seemed very crummy. I've never been a huge fan of previous SS games (or Painkiller, really), although I do like Doom and earlier Quake games. I think if I bought it it'd be on PC, but I don't think I'd buy it.