halo 3:odst or halo wars
He doesn't want a list of different games that you guys like. He only wants your opinion on two games. If you think they both sucked ass and recommend another game, just don't, because he doesn't want that. If he did, he'd tell you so.
HaloWars
Personally, I found that Halo Wars was a good game. Of course it's not really going to stand up to any RTS on the PC, due to it's limited amount of controls and what not. But generally, the story is good, the playthrough is good, the easiness for control is good, and it has some great minimovies in between missions. If you're into an RTS then I'd say it's quite good. The units are all fairly averaged for each other, and the Enemy AI is quite good. The story is long, and planning and working out strategies for matches gives you a fair amount of time to play without it getting stale.
Halo3:ODST
Halo ODST on the other hand, gives you a relatively short story compared to any of the other Halo games.
The fact that you're no longer playing as the Chief or Arbiter makes the game interesting.
As Rughugger pointed out, you can't just jump in lob a grenade and shoot in a circle anymore.
The game actually requires you to think about what you're doing a bit, instead of charging in gun-hoe.
Although the story line is short, it's really quite interesting.
There aren't any new weapons in the game, so it's easy to play and get used to if you've allready played Halo2/3. If anything, the only difference in weapons is the Plasma Rifle is Red*. Although if you played Halo2 you'd know that the Brutes had Red Plasma Rifles and that's who you're generally up against in ODST.
Just a note, don't go charging in for ODST if you think it gives you all that Halo3 does.
The game only has three modes on it.
Campaign: The Campaign missions.
FireFight: Surviving hordes of enemies attacking you on your own or on a team
Theatre: Watching films of your previous battles in Campaign or Firefight.
So, if you're looking for new Forge material or some online Custom Games, this is the wrong game.
However FireFight holds up for some good fun with friends. Attempting to see how long you can survive against hordes of enemies, who slowly get harder each wave, and skulls being added too.
Obviously as Xbox360 games they both have achievements, but with ODST if you complete certain achievements you can unlock awards via "Halo:Waypoint" providing new "Clothes" for your Avatar.
The Achievements on ODST also work with the ones on Halo3, in the case that, completing the VidMaster achievements on both games unlocks you "Recon" armour on Halo3, which previously could only be given to you for something that Bungie deemed impressive.
Surprisingly, I've had HaloWars for some time now (Since it came out, even)
I've only had Halo3:ODST for two days now, and I managed to write a lot more.
