Art is subjective sure. But you're still missing my point.
Even the snootiest art critic would have to admit the different between an experienced artist of decades working in his field and someone thats just started out is a world of difference.
Skill goes into making a video game. When you play a game, you really get a since of how much work went into it. Example, Mass Effect. They concentrated a lot on graphics and making it pretty, but the game has a lot of bugs, and the levels are very repetative. It's a 7 or 8 out of 10 when it could have been a 10 out of 10 if they worked on it longer. Halo 3, feel free to disagree but I'd say BS, the levels just aren't very good. They're too short and not very varied. The game overall is very short. And throughout the whole game its the same thing - bang-bangbang-bang. The only change of pace is when ya use vehicles.
Whereas with Half-Life 2 and it's episodes, I'm blown away by how clever the game is. It's not as pretty as Halo 3. But the game even without the episodes is much, much longer. The game is definately more varied. The action constantly changes, you never really know what to expect next. The scripted sequences give it a feeling of an action movie (like dodging a train, etc). The gravity gun is great and makes for interesting gameplay. They design the game in such a way as that when the action kicks in you're always on the move, the pace is constant. They really know how to move the player along. The levels are varied and different from each other. There's puzzle solving which is just about perfect - not easy, not too hard. At the very least, ya gotta concede Halo 3 is short and Half Life 2 is long.
If it were completely down to taste and opinion, why do most reviewers point out the exact same flaws and praise the same things? There must be definite markers of quality.