Rexaura is a mod for Portal based on high energy pellets and several new mechanics surrounding them.
Rexaura is pretty much the best Portal mod in existence. Put simply, it's a bunch of Valve quality test chamber maps with a continuation of the wry and nasty sense of humor that ran throughout Portal.
If you liked Portal and want more of the same, this should be your first port of call.
A very challenging but very thought out portal mod, just like Portal Pro this mod is a masterpiece of puzzle solving. Was hoping for some more story based ending, but personally that is also forgivable. Did often come across annoying glitch though where I get killed the moment I go through a portal devoid of nearby hazards. Finding the third bonus cake was pure evil, don't ever make something so tedious again.
Map design: Excellent
Voices and humor: Excellent
Use of custom content: Excellent, even though there wasn't too much new. It was good that the original Portal feel was kept.
It was so tempting to find spoilers for some of the puzzles, but I managed to do them all without cheating. It took forever. I almost never do that for puzzle games/mods but this was well made and it was worth it.
I normally don't give 10 to puzzle-only mods but I honestly can't find any reason to complain about this. :/