Pretty much everything has been said about the game, but I'd like to a little bit of what I think.
When you said Halo 2 requires no skill online, did you think for one second about the asymmetrical CTF maps that are supposed to be so challenging, and when you said that it was geared for n00bs, I take it you are Johnathan Wendell's guru, and if you are, then maybe, just maybe, I will accept what you say.
BTW, one thing has been really nagging me. Where on EARTH did you get to play Halo 2 online? Did you travel just for this to a country that has the XBox Live service?
HL2 has simply the best gameplay on the planet, period. Whether its using the ZPEFM
D) to use the environment so you can advance in the game, rip zombies in two with saw blades and toss Combine soldiers into disintegrating energy fields or pushing down washing machines onto lifts to create makeshift ramps, HL2 has the most usable physics engine in any game ever created. All you did in Doom 3 was use explosive barrels.
And compared to the original, WTF, you cant even compare it to the original, the Water Hazard, Highway 17, and the last seven levels, standing on their own, were better than a hundred "Surface Tension" levels from HL strung together. (Honestly, when was the last time you saw squad tactics in a pure FPS?) You're right, its not even close to the original - its a billion, trillion, gazillion times better than it.
True when it comes to monsters, HL does have a lower monster count when compared to Doom 3, almost half the number, not to mention there are no end boss monsters (which was truly weird for HL2, even if it was a prequel to HL3 and just half the story like Matrix Reloaded to Revolutions) but they're still great, not to mention that they have the highest polygon counts ever in a game, for the lucky people with an X800 to have gory fun in "We don't go to Ravenholm..."
No gameplay variation, you say? You move from a civilian to a Messiah, using every possible means of transportation and every means of help possible from human, machine and alien, and use every means of transportation and travel between every setting from an urban city in ruins to dingy canals to extensive waterways to dried up oceanbeds to a warzone to an alien Citadel and have every weapon from a measly crowbar to an ultra-power-boosted GG. What more gameplay do you need?
Like gamefreak said, all that drove me in Doom 3 was the graphics engine, and there was no gameplay to speak of. I just loved getting scared (which was the first ten times or whenever a new monster came up) and mindlessly using the Soul Cube all the way from the second level to the end boss in Nightmare mode. I even used killmonsters in one level because I was so bored.
I know D3:RoE should change all that, and I hope it will and I especially look forward to using the Hunters' abilities to warp time, etc. for my own exorcism rituals.
