Unreal - if you want fast paced, arcade like action.
Counter Strike Source - if you want fast rounds/matches and don't mind not being able to respawn...and a game generally full of 14 year old a-holes. Small maps.
Star Wars Republic Commando 2 - if you want hella fun, intense single-player missions. Very chaotic multi-players with mindless gunspraying.
Joint Operations - if you want a sense of realism, various tactical game types, vehicles, and 64-100 player servers. LARGE MAPS! Closest game to actual war imo. THE BEST stat tracking fps you will find. (personal fav)
Battlefield 2 - A lot like Joint Ops, but a little more arcade like. 90% of the player base are a-holes too.
Delta Force: Black Hawk Down + expansion - This is by far my favorite. Nice gametype choices (deathmatch, team deathmatch, koth, a&d, flag cap, etc) Good if you want something a little less chaotic. No vehicles. Run, shoot, kill, die, and spawn. Does take some tactics on some gameypes, but not nearly as much as largscale games like BF2 and Joint Ops. Great stat tracking, but not as detailed as Joint Ops. Oldest game on the list, but still amazing.
Delta Force Xtreme - This is the most simple out of the mix. No certain class to choose (medic, gunner, cqb, etc) Just pick your weapon and go kill...die, spawn, then go kill some more. A few gametype choices, but it's usually the TDM, flag caps, and TKOTH maps that are full.
Ghost Recon Advanced Warfare - Very realistic and tactical squad-based game. Maps are large and pretty much all urban warfare (Mexico City). Server selection is lacking, and I see no stat servers.
Call of Duty 2 - If he likes WWII setting this is the game. Not good for anyone who likes the modern weapons and warfare. Hella fun though! Face paced, close quarter maps.
It really all depends on your brother's playstyle. Some like a ton of vehicles and huge maps...some like small maps with close combat. Some like games where you can respawn, some like it better when once you die you wait for next match (Counter Strike).
As for me I will always stick with Novalogic games (Joint Ops, Delta Force BHD, and Xtreme) because they are the only games on the list that have their own detailed stat tracking feature and host their own official stat recording maps. You can login, join an official server, and level up. Closest thing to MMO as far as leveling up goes...though all it earns you is a new rank and some respect
I like it because I can look back at everything I've done, unlike other games where you have nothing to show for as far as what you've accomplished. They also have tons of awards you can earn.
Here's a link to my
Black Hawk Down stats
Stats to the end of a
BHD map(I'm kov.art). As you can see a game where you can rack up kills. (ok, so now I'm bragging)
NOTE: I think some of the other games (BF2) have some stat tracking, but it's up to the people hosting the server to provide it. I could be wrong in this. Someone clear it up if they know. I just know that all the Novalogic games keep their full stat tracking on Novaworld.com.