Not to say that the movies are themselves gratuitous ... well, OK, I take that back. They mostly are, in different ways. None of them are Brand Shiny New; indeed, Shaun of the Dead came out in 2004.
Let's start with Shaun. Yes, shocking though it may be, I'd never seen it before this weekend. Based on what I'd heard from people who've seen it, I was expecting zany zombie-attack spoof along the lines of Evil Dead/Army of Darkness. Instead, it leaped directly and effortlessly into first place in the list-of-dishonor of The Stupidest Movies I Have Ever Seen. There is basically one likeable major character in the entire movie, Shaun's girlfriend Liz; essentially all of the remaining leading characters are so utterly, brain-damaged THICK you spend most of the movie wishing they'd just hurry up and DIE ALREADY and get it over with.
Liz is, in fact, one of only two likeable characters in the movie who don't end up turned into zombies. As it happens, both of them have at some point or another dumped Shaun, in Liz's case (at least) because he's a complete loser. There's a lesson here, although the other ex-girlfriend, Yvonne, doesn't seem to have learned it, as her current boyfriend seems to bear an uncanny resemblance to Shaun ... or maybe, even worse, to Shaun's totally brain-dead best buddy Ed.
There's nothing funny about Shaun of the Dead; it's just embarrassingly stupid. I spent almost the entire movie thinking that surely, with everything I've heard from friends about how funny Shaun is, any moment now it had to kick over and make a transcendent leap from stupid and tedious into brilliantly-inspired over-the-top satire. But not only did it never achieve the leap, it never even showed any visible sign of attempting it.
Overall rating for Shaun of the Dead: 99 minutes of my life that I will never get back.
Next up, chronologically, is Igor. Yeah, as IMDB says, it's pretty clichéd. And for my personal tastes, it loses major points for including musical numbers (or parts thereof); but I'm willing to forgive that, painful as they are, because for once they actually are part of the plot, rather than being the pro forma gratuitous all-singing-all-dancing revue numbers that have featured in pretty much every Disney¹ animated feature since, oh, the invention of cuneiform.
Still, it's a fun romp, even with the clichés, not least because — unlike Shaun — it quite unabashedly lampshades its clichés and enthusiastically paints them all over the fourth wall. There's no particularly original storytelling here, but still, it has its moments.
Overall rating for Igor: Fun entertainment in the style of The Nightmare before Christmas, even though it fails to reach Nightmare's level.
Last up for this weekend, and newest of the list, is James Cameron's Avatar (as distinct from Shyamalan's "Oh dear god please let there never be another Airbender"). First and foremost, technically speaking, ZOMG, the pixels are shiny. I'd say Avatar is worth watching even if for no other reason than to appreciate how good full-motion CGI has become. The production of Avatar was actually delayed by several years because the CGI technology wasn't good enough yet; Cameron wanted the CGI to be photorealistic, and it is, although some of the movements of the Na'vi — particularly their tails — are sometimes subtly not quite right. We're not quite at the point yet of being able to replace human actors altogether, but it's clearly coming.
OK, the story's not what one could call totally unexpected. In fact, it verges on formulaic, though it's not quite the Pocahontas-with-the-serial-numbers-
Aside from the cheerful lampshading of unobtainium, the science is all within willing SF-setting suspension of disbelief as long as you're willing to accept the never-explained flying mountains as "A Wizard Did It". The technology is distinctive, and mostly plausible for an SF setting aside from a couple of glaring exceptions. For one, while the design of the VTOL ground-to-orbit spaceplane is clever, it's clearly a cargo and passenger hauler never intended to be used in combat, and it's all but impossible to come up with a rational explanation for it having an open, manned dorsal gun position except to provide cannon fodder for Jake to kill before he destroys it. (The best that can be done is to speculate that the gun position was improvised on-site to give some minimal pretense of defense against aerial attack to an otherwise completely unarmed vehicle. In that case, though, bringing it to the attack more or less in the van without even ensuring air superiority first can be attributed only to blind, arrogant overconfidence ... which, to be fair, GI Joe — er, I mean, Colonel Quaritch — has in spades; and given that they flew it in amid a cloud of attack choppers, one has to wonder why they even bothered rigging the gun position.)
Also, while the attack choppers with their dual ducted contra-rotors are plausible and interesting, if one uses them as a baseline for the lift-to-size ratios achievable with the then-existing technology, then there's no possible way the massive walker-suit drop carrier/bombardment platform with its few relatively tiny ducted fans can be generating enough lift to leave the ground at all, much less stay in the air. (We'll handwave as artistic license the physics problems inherent in the idea of a several-thousand-foot fall in a clearly-multiple-ton powered walker suit with no visible or apparent ability to fly, terminating in an upright landing on a surface sufficiently firm for said walker suit not to embed itself fifteen feet into the ground on impact, being surviveable² either for said walker suit or for its pilot.)
Overall rating for Avatar: Typical action-movie-level entertainment as long as you're not expecting Robert Ludlum depths of plot. Shiny, shiny pixels really showcase what's possible with current CGI technology.
 Note that I do not include Pixar in this category. Pixar does good work; Disney largely just bought the right to put their own name on top of the credits for Pixar productions, and I'll give them credit for having the sense to mostly keep their hands out of Pixar's production process.
 Bonus points for back-of-the-envelope estimation of probable terminal velocity of the walker suit and probable Gs of deceleration on impact. Keep in mind that since the walker didn't visibly either embed its legs into the ground at all on impact, or bounce, said ground can reasonably be considered both rigid and inelastic.