The only reason H2 and 3 were so popular is because there was virtually no competition. They would get smacked around in today's market.That is completely false. A quick Google search will provide you with what games came out in 2004 through 2010. There was high competition during that time period, not sure how you can argue against that. It just shows how popular Halo was during that time, being relevant with all of the great games that came out in those six years.
Not really false at all.
If you played online on a console, there were only 2 shooters that mattered: Halo 2 and R6: Vegas. The latter being quite a bit too hardcore for the majority (read: mainstream) gamer. The first being the best and most progressive console FPS you could get. Other FPS games didn't matter on consoles, until H3 had to face off against CoD which began stealing mainstream appeal from 2007 onwards. Up until then, even though CoD2 was treated as a 360 show stopper, CoD had very much been a PC series.
Halo had a lucky combination of being:
1: Ridiculously good at the time of H2.
2: Having competition that was still stuck in 90's game design.
It was popular with a wide range of gamers. But as always: mainstream gamers determine if a game is super successful or not. They flocked to Halo because it was the thing to play. And then came Modern Warfare.