Choplifter HD is only recommendable to people who don't mind a severe "old school" challenge. Everyone else will probably find the game too frustrating, even on the lower difficultly levels.
Like the 1980s original, Choplifter HD puts you in control of a helicopter and tasks you with rescuing people and bringing them back to safety. Enemies dot the levels and they'll take shots at you; if your helicopter takes too many hits you'll blow up. Likewise, if you run out of fuel, you'll crash. Choplifter HD becomes a game of risk management; do you have enough fuel to make it to the next person who needs to be rescued, or should you turn back to refuel and repair first? The clock is ticking...
All of this is fine, and is keeping in the spirit of the original game. Where Choplifter HD veers off-course is in the difficulty: this game is tough as nails. The first two or three levels are easy enough, but the difficulty spikes severely from that point on. Levels are jam-packed with enemies that can take your health down in a flash and many of them re-spawn after a short time, meaning you have to deal with them over and over. Enemies with RPGs and EMP rifles that stand on rooftops are very hard to spot, and later on you'll have to avoid missiles fired from jets as well as incoming mortar fire. There are even tanks and AA cannons that can take you out in a couple of hits. It's almost impossible to avoid taking damage in Choplifter HD, so get used to restarting some levels multiple times before you finally conquer them.
If the campaign becomes too much to take, Choplifter HD also has a zombie mode: here, you fly back and forth across a besieged city, shooting zombies and rescuing people. It's fun for a while.
One other thing worth mentioning: the awful voice-acting. Throughout Choplifter HD, you'll be treated to poorly-written and voiced jokes and one-liners from your chopper's crew. None of the jokes are funny, and they're repeated over and over. Some of the dialog is surprisingly tasteless too. Turn your speakers off.
If you're one of those people who think that modern games have become too "casual", then Choplifter HD is for you.