The original game becomes a jumble of pixels quite often. There’s a source port, though, that addresses that issue:
Also curious that the original game ran in 320×200 resolution. That’s why some of the DosBox screenshots look a bit off.
Think you haven’t suffered enough? 3rd level introduces a generator of enemies. Luckily it’s not infinite, it seems.
And on the 6th level, a new horrible enemy appears. A hitscanner. Prepare to die to its chip-damage.
The red hulks start apear more often here as well. And their homing missiles are almost impossible to avoid. I thought previously I didn’t know flares existed. But flares seem to have no effect.
7th level seemed easy at first. Until I reached the final room. I vaguely remember playing this game as a kid that there was some kind of invisible boss that shot homing projectiles at you, and I never managed to beat him. But I thought it appeared earlier in the game.
Death is not the end, though. Despite the game having a proper save/load, it also has a lifes systems. After being killed, you respawn at the beginning of the level, having left all your equipment where you died. Kind like MMORPGs. The only downside is that you loose all the hostages, if you picked any.