Hard to single one out. I've always cited Halo 2 as my favourite, but only because it dived further into the Covenant's elegant style more than ever. Otherwise, it's not really that unique. Sure, it made the human military more appealing with greens instead of just browns and greys, but that's not my favourite part of Halo art, and neither is the Covenant. That, my friends, lies with the Forerunners. CE pretty much perfectly captures the epic yet mysterious presence of the faction, with gargantuan structures that yet lay almost entirely dormant. And the pallet of the Forerunner structures and interiors was fantastically executed, as they had both this futuristic lustre to them, whilst looking impossibly ancient and leached of colour by untold centuries of existence. Unfortunately, CEA -blam!-ing butchered this by adding bright lights and unnecessary angles all over the -blam!-ing place, making the ringworld look busier and therefore less quiet and mysterious. Conversely, I adore H4's art style (not as much, mind) because it went in a really strongly futuristic direction, with much more inexplicable technology in the form of all the floating Forerunner doodads and lights and protrustions and stuff. Sure, a lot of the surface detail was unnecessary noise (see how 343 -blam!-ed up the Reclaimer symbol, although whether they could just use the Marathon logo as Bungie did without running into copyright laws, I don't know), but 4 was a noisy, bombastic, punchy return for John and Cortana, and that really shows in the aesthetic. Whilst 3 didn't really add anything, just tarted it up for the seventh generation (I did -blam!-ing love the Ark, but mainly because of its size. Though the whole scifi heaven thing is delicious), Reach is definitely my least favourite, taking the beautiful, colourful universe and dragging it through the goddamn mud until it looked like yet another brown-n-grey military shooter. I'm glad 4 brought Halo's unique colour pallet back, and I can't wait to see what 343 does with 5/(2014). What does H2 have going for it if not the art? Well, art isn't limited to visuals: H2's music is the best in the series, and without Marty anymore, it probably always will be. The plot is also the series best, so far, although CE and 4 are both pretty damn awesome.