Last night R-Type Dimensions showed up on Xbox Live Arcade and I picked it up. It's a port of R-Type and R-Type II with the addition of 3-D views, an infinite lives mode and online co-op.
This game is hard-core. Casual gamers need not apply.
I finished it, but only because I played in infinite lives mode. Had I played in normal mode, my three lives would have evaporated within seconds.
I did notice one bug: From time to time, while playing in 3D view, the game will switch to 2D without user input (you can use the Y button to switch). Minor issue, but annoying.