I've been playing the Battlefield series fairly religiously since Battlefield 1942 almost 10 years ago. I even played the predecessor, Codename Eagle - although that's not strictly a Battlefield game. I ended up playing Battlefield 2 on and off (more on than off) ever since it was released. I even played Bad Company 2, and it was alright. One of the main differences between my enjoyment of Bad Company 2 vs BF3 was that I was not hyped up for BC2 - I knew what it was before I bought it. I was sorely mistaken in thinking that BF3 would be a return to DICE's roots.
The series was seriously revolutionary - things we take for granted now were pioneered (or at least perfected) by prior Battlefield games. It seems like BF3 is a step back in every way except graphically.
Step forward:
Graphics - It looks like a polished BF:BC2, which isn't surprising since it's using a polished version of the same game engine. Nice to look at though!
Sound - It sounds great!
Step backward:
Squads - The BF2 squad screen just made sense. You could name your squad (ie. Armor, Tanks, SNIPERS, Infantry, MICS ONLY) to give people a clue as to what your squad was looking for. My personal opinion is that we have such a limited squad UI is because it was written that way to cater to the console audience, and forking something like squad management would add too much overhead for their future patching/DLC.
Communication - Oh god, it's awful. Just awful. No built in VOIP? Why? Some of my best (online) friends that I still play with in other games I met through BF2 squads. The joy of finding a squad you worked well with and communicated with made for some of the most intense virtual firefights I've ever had. Sure, the lens flare in my eyes might be super realistic (since I wear glasses in real life so I experience lens flairs - I can only assume that every US and Russian soldier in BF3 has awful vision and are all wearing glasses too) and that RPG flying over my head might look more authentic, but if I can't hear my squad mate shouting for backup, or warning me of an enemy flanking maneuver, or just cursing into his microphone as a grenade lands at his feet, it feels much more hollow. BF3 - for all it's auditory and visual stimulation - feels less realistic than BF2 for me. Just for the lack of human interaction. I might as well be playing with and against bots of varying degrees of intelligence.
Modding - This is just the times we are in. Allowing people to mod means that enthusiasts won't make for free what you can sell for $15. Any other excuse like 'the engine is too complex' is crap. Every new generation of engines is increasingly complex to mod - but every time, modders adapt and create amazing works for them. Compare the Unreal 3 engine to say... modding Quake... I'm pretty sure people managed to adapt.
Maps - The maps feel smaller to me. Even the large maps. In BF2, I found plenty of action *between* capture points. For the most part now, in BF3, most of the action takes place in the same few places. Maybe you could call the map flow or map direction, which is great for a more intentional structured game play (such as in BF:BC2), but seems out of place in the dynamic open maps of BF2/1942. This illusion of smaller maps isn't helped by the fact that the large BF3 maps range from 3-5 capture points, while the large BF2 maps ranged from 6-10 capture points.
Commander Mode - Uh, it's gone. I'd say that's a step backwards for something that was a fairly revolutionary feature of BF2.
Origin - I hate it. I already have Steam, which I resigned to use simply because so many games *require* Steam. Steam has also proven itself to be largely non-invasive - its features seem more beneficial and less intrusive. Unfortunately for EA, BF3 is not the game that will force me to use Origin. I've uninstalled it, and seriously regret ever signing up for an account. I'm not going to list every problem I have with it - a simple Google search or a read through these reviews will tell you the problems. Even if you imagine that only half of the problems listed are genuine, that's still too much for me.
Other minor complaints are a very lackluster and non-intuitive interface (although if I imagined myself using an XBox controller, it started to make sense), the web based server browser was ugly and slow (having to restart the entire game to swap servers? Come on!), the chat box is mostly useless, and the game is severely hampered by individual unlocks (leading to a COD mentality of "I'M RAMBO" rather than the older BF mantra of "Let's at least pretend to try to win as a team").
If Origin weren't so invasive (or I could have the game standalone/on Steam) *OR* if the game were truer to the original Battlefield series, I'd probably still have it installed. It's the combination of mediocrity on the part of BF3 and utter crap on the part of Origin that led me to uninstall it. I tried. I really did. I gave it over 2 weeks, and in the past 3 or 4 days I just have not found myself wishing to log into Origin or BF3 at all.
My only hope for this game would be mods, but I doubt they'll allow that with the lucrative cash cow that is DLC sitting in their laps.
Final thoughts: If you want a hybrid of BF2 and CoD:MW2/BO/MW2, taking the slower strategic/tactical parts out of BF2 and adding the run'n'gun/unlocks/achievements/lonewolf style of CoD, then you will really enjoy the game and I can't recommend it enough. For some of us older gamers who never got into that sort of thing, I'd have to warn you away.