Before I get to the good changes though, there is one bad change, and it's only supports 1 player. This is because a large percentage of PC players play solo (if they're not online), and that simplification let me make some changes that otherwise wouldn't have been possible.
Inferno+ is the most demanding of your graphics card's shader abilities.
Any Nvidia and ATI card made in the past 7-8 years or so should be fine, but some Intel-based cards may have a little trouble.
You'll notice I said "remixed" above. What that means: All 30 of the original levels have had modifications to their layouts. As an example: the first level shown is level 5. Though the outer dimensions of the level are the same, the flow through it has changed quite a bit. So even if you've played through the XBLIG version of Inferno multiple times, playing the first 30 levels of Inferno+ will still be fun and exciting.
In addition to the remixed levels, there are 10 all-new levels. Those are levels 31-40. I don't want to give too much away, but the last sequence above is from one of those new levels.
There are 2 all-new enemy types and one new turret type, plus 2 new bosses. So now the bosses are on levels 10, 20, 30, and 40. Every 10 levels also has its own color scheme and song now. Add it all together, and the progression through the game just feels better. For New Game+, every level gets extra enemies that aren't there normally (along with some other tweaks).
For the player, there are 10 upgrade slots instead of 8. One of the new upgrades is to increase number of drones (from 1 to 2 to 3), and the other is for shots to do a stun+push. New ship abilities: Shots can be reflective instead of homing, and the shields can do damage to nearby enemies instead of pushing them. You choose 1 of 4 ship configurations to select between homing/reflective shots and repulse/electro shields. It costs a small amount of gold to change between the ship configurations.
Control-wise, everything is reconfigurable. Though I wouldn't recommend them for the hardest difficulty level (Volcanic), mouse and keyboard controls work very well.

SYSTEM REQUiREMENTS:
Mac OSX 10.4 or later
Graphics card with 64MB or more VRAM