Some things Halo 2 had off the top of my head that aren't related to gameplay:
- Matchmaking. Almost all games at the time made you manually join lobbies, and now we take matchmaking for granted.
- Persistent party. You'd invite your friends to your party and then start the match-making process. During the whole process you could chat with your friends, and when the game ended, you were still a party and could talk to each other.
- Chat. Everyone had an Xbox Live headset which came with the service. So everyone was a participant of party chat, in-game team chat, and even "proximity chat" with the enemy. With Halo 2's chat systems + Xbox Live headset ubiquity, it was a highly social game.
- Split screen online. All of the above worked with playing with a friend in split screen. Your friend could come over and you could start Team Slayer matchmaking in split screen which was awesome—the game would have to find two more teammates—, and your guest could even chat. Something that could never be done on PC really.
These dominated the old "look for and join the server" model of past FPS and, frankly, I could never go back to that.
Gameplay wise, Halo 1 had most of the innovations that Halo 2 capitalized on but Halo 2 moved to the pure shield-is-your-health-bar system and removed health packs. After each battle you didn't have this scramble for a health pack just to get ready for the next confrontation, so the pacing was better than arena shooters imo.
Finally, Halo 2 didn't need to be the global first on each bullet point to be innovative. But it was probably the first game to have all these in one package. There was a lot of UX polish in setting this standard which you can tell because most games don't reach it even today.
A lot of people lament the death of community run dedicated servers, but I'm with you here. I don't miss trying to find a good deathmatch UT04 server that wasn't either super high ping, loaded to the hilt with obnoxious mods, or stuck running Rankin 24/7, only to give up after 40 minutes.
Oh wow, I had totally forgotten about server hunting.
I kept a list of "good" servers (based on ping, map rotation, who played there, mods, etc), but when they were empty finding somewhere else was a complete pain.
I miss the camaraderie on some of those dedicated servers, but I know I wouldn't be able to get into something like that these days.
I think a lot of that camaraderie and sense of community has moved to places like Discord and Reddit.
I have a group that regularly plays Overwatch together every Friday. Whenever more than 5 people show up, we play custom games. The workshop is surprisingly powerful, so it even gives us some of the experience we used to get with mods for games like Quake and Unreal.
When we have 5 or fewer people though, we really appreciate the game's matchmaking, even though it is far from perfect. It is a lot better at creating balanced matches than any server auto-balance feature ever was, while always keeping us on the same team.
Games like tf2 make parsing community servers pretty easy. You can do things like set ping cut offs, only look for nonempty and not full servers, look for certain numbers of people playing, certain maps or gametypes, and include or exclude keywords like certain modded gametypes.
At least then you could run your own server with whatever settings you wanted. Now instead you are left with unplayable games because the developer or publisher decided to shut down the servers.
Don't forget the post-game carnage report, which, while first present in Marathon, was refined and provided the best post-multiplayer-game stats of any game I've seen, even years later.
The telemetry bungie used to popular stats on their website is better than pretty much any modern game today outside of like CS2. I will caveat that by saying modern practices require you put things behind an api with a paywall of some sort, but they had freaking action heatmaps in 2004.
One thing that halo and some other games do is let you thumb through the last matchs stats while the next map loads. Valve games just throw you a map loading screen you’ve seen a thousand times.
I had interpreted the parent comment to be about gameplay, but those are all fantastic points about matchmaking and the related QoL improvements. It absolutely is taken for granted because I forgot Halo 2 was the first to do _all_ of that well, and in one complete package.
In what ways exactly? Competitive online FPSs with strong modding communities were already more than a decade in full swing on the PC.