The one thing I don't like about Half Life anymore is that some of it is just archaic now. If they were to simply put in iron sights, then I may like it like I once had. It's something some may see as minor, but it can help a lot. Half Life 2 was certainly a lot better around the time it came out, but in 2007, I played through the Orange Box, and I didn't enjoy it as much as other games that came out around that time.
It was unfortunate because previously, Half Life 2 wasn't only my favorite shooter, it was one of, if not my favorite game of all time. There's still a lot of impressive stuff in it though, it's just the way you shoot without iron sights, and the sprinting is kind of awkward, little things really that add up. I loved the original Half Life 2, but by the time the two episodes came out, I was kind of past Half Life 2 in some ways, and those from a setting perspective initially disappointed me.
When it comes to the original Half Life, I didn't particularly like the shooting in that, and while I loved Black Mesa, there were more areas in the game that were dull and unpleasant than entertaining. I hated the moment where you get the crossbow in the game, the environments were kind of ugly there. The Half Life games in my opinion though are in no way bad or mediocre, they just need to get with the times some while being unique at the same time.