Gears of War
1. Gears of War III - I felt this easily had the best multiplayer in the series. The new weapons and fast pace kept it from getting stale and added new tactical dimensions. The campaign is only slightly less epic than II and although I felt the Lambent were a lazy choice as the new primary enemy this was still the overall best entry to date.
2. Gears of War II - Possibly the biggest divide since Kirk or Picard. What's better Gears I or II? I have had long discussions on the topic and I firmly believe Gears II was a sound improvement over the original. The campaign is as emotional as it is epic and the multiplayer received much more refinement. After playing the entire series I can honestly say II left the most lasting impression.
3. Gears of War - I have a love hate relationship with the original. It's a great game that spawned my favorite shooter ever. The campaign is brilliant and set the bar high for the competition. That said I found the multiplayer initially unbalanced (active reload snipe, two piecing) and the overall enemy AI inconsistent. Having RAM get stuck behind cover, endlessly walking in place not firing his weapon made a easy kill (The first time I fought him no less) and similar quirks throughout somewhat soured my initial playthrough).
4. Gears of War Judgement - No surprise here! This is the Gears franchises answer to "Reach". Instead of providing a fresh prospective and upgrading the multiplayer like Bungie, they decided to water down and nearly ruin the famed multiplayer experience altogether. While not bad by no means the campaign (Which featured two of the best characters) seemed to go out of it's way to shackle them. Cole especially seemed quite tame and barely fleshed out as the second lead. I also found it to be extremely anti climactic.
Halo
1. Halo 4 - I have long argued Bungie made it's characters far too shallow and focused purely on the multiplayer and blockbuster visuals (Sound familiar?). 4's new direction gave the chief a soul and more importantly managed to tell a well paced and emotional story. I have high hopes for the next two entries in the new trilogy.
2. Halo Reach - Okay so I know I'm going to take some heat from the purists here. I felt getting away from the one man show space opera that became 1-3 was a good move for the franchise. This actually had a good cast of characters and was a nice change of pace overall. The changes to multiplayer caused quite a ripple in the fanbase but "Combat had to evolve". Without Reach you can argue Halo was getting quite stale.
3. Halo - The game that saved Xbox! Not much to say about this one. It had a good story and looked great in it's day.
4. Halo 2 - The original was a tough act to follow. The guess the only thing they could do was completely revolutionize online gaming...while normally this would plant them higher on the list I did not care for the campaign all that much. I plan on replaying this soon for a second take on it's story.
5. Halo 3 - Quite possibly the most over hyped game in history. Bungies marketing team deserves a lot of credit as even my Mom knows what Halo is thanks to them. I'm currently playing through the campaign now and so far it feels slightly generic compared to the other entires. I dabbled in the multiplayer like everyone else when it came out and felt it polished the formula to perfection but left me wanting more creative changes.
*I have never played ODST or Halo Wars but own them both now so I left them off the list until I get a chance to beating both*