I'm not Half-Life's biggest fan or anything. I didnt like the first game much. But HL2 is definately worth taking a look at. It's fun and interesting and any gamer should at least give it a whirl once.
One caveat, HL2's fans played it when it was new. So things that they loved will not blow you away in todays market the way it blew them away in 2005. It's the same with us Hardline Halo fans who were blown away by the first one. People who didn't play it when it was new don't get why we go on and on about it. It's just human nature to remember things that you've enjoyed fondly. Rose-tinted glasses and all that.
The bottom line is that HL2 has aged well enough and any gamer should at least give it a try. The see-saw puzzles aren't going to blow you away since every game worth its salt has a physics engine nowadays. But go into it with an open mind, remember that it's over 5years old, and I'm sure that you'll get more than ample entertainment for your purchasing dollar. If you like good games, you could do much much worse. If I were a betting man, I'd put money on you having a good time playing HL2 and its episodes 1 & 2 expansions.
All that said, Mass Effect doesn't even play into the equation. I see no relevant comparison in gameplay or story structure. Contra had guns as well, but I wouldn't let it play into your buying decisions regarding HL2.
