[1] Ah yes, about to retire, it's obvious you'll be dragged back in to the fray, etc, etc.
[2] The water-for-fuel[3] concept is an old cliche. Even the animated Dan Dares did it. Water is the stable oxidising product of some decent fuel components, however, which means you need to put an awful lot of energy in to get something (at least in chemical terms) that you can get not-quite-as-much energy out again. And which, having been 'spent', could be re-reversed. If it's not a chemical process, but possibly
2H and/or
3H fusion or something not even understood, then that's something else and that TV expert might well have been completely missing the point, albeit consistently within context of B:LA's fiction.
[3] To he who said "why not go for the frozen water moon, instead", I think the film tried to address that by the TV expert (who must still be treated as an unreliable witness, given that this character is only 'intelligently speculating') saying how we were the only place with liquid water. Maybe they couldn't spare the energy to warm up Europa's ice, and moreover couldn't wait for the few years needed to more indirectly suppress the indigenous population (us). Could be that they're on the run from their equivalent of the Cylons and need the water
now.
[4] Why does the HST keep getting drawn into these things. Using Hubble to look at the incoming objects (which were apparently "only spotted when entering the atmosphere" but, even if they weren't going at terminal velocity when hitting the ocean, they took an awfully long time to crash down) is like trying to use a binoculars to identify the spin of the incoming ball when you're in a game of cricket/baseball and holding the bat. You probably couldn't even focus. (Plus, back to the "only when they enter the atmosphere", that means Hubble's point backwards, or at least looking through the edge of the atmosphere from most of the way around the planet.)
[5] Alien biology being quite a bit different from us (and enhanced in the manner of cybernetics) was good, but them being largely bipedal (except for some of the more specialist units, including the quadrupedal weapons platforms) just didn't work well. And I prefer movies where there's far more mystery. And why didn't they tag on "Oh, and shoot them just to the right of the heart, Ok?" in the first communication to the outside world? Or did they send this information out when they got that internet link in that store? AFAICT, there was no attempt to do anything but listen to the reports.
[6] Alien drones hovering using fuel-burning pulse-jets (
not obviously hydrogen-oxygen flames, either) seems to me a bit energy-inefficient for supposedly energy-deficient aliens, but you can ignore this if the expert was wrong. Personally, I think they were draining the water from the planet so that they could populate more of the Earth without their exoskeletons rusting, plus dehydrate into extinction any isolated pockets of native fauna and maybe even in the process create an ice-moon of their own, in orbit around the planet, shaped to resemble their favourite alien Soap Star's face... Not
that would be a megaproject.
[7] They take the humans by surprise a number of times and on
most occasions, completely fail to wipe out everyone. Even with heavy artillery, which they then proceed to plod forward with, bringing it into danger. They should have known long before the bus exploded that
these humans, at least, was very good at picking off the foot-soldiers and just stood off and blasted away from a position proven to be within range, rather than almost casually plodding closer and closer while applying nothing more than a fairly lacklustre amount of suppressive fire, given their standard infantry armament. Indeed, quite a lot of time the humans saw the shots coming towards them and dodged. Or spent time helping someone else to dodge. Or had time to actually arm themselves (from scratch, and without any obvious previous experience with the firearm) and do damage, albeit in this case not quite avoid the return fire in this case (although given he had no body armour, it's a surprise he wasn't cut in half immediately). Only the first rescue helicopter actually succumbed to a surprise attack. I won't comment much about the original FOB's distruction, because who knows what was actually sent in to overrun it, but to find a pair of essentially unscratched vehicles left? PLOT PLOT PLOT!
[8] You know what I wanted to happen. I wanted them to work out (eventually...) that those glowy things sitting in the water were the actual hive-mind controlling objects that they needed to knock out, mainly by kicking each one over, making the alien drone response gradually more and more stupid. Instead, I'm sure that their probable purpose was of somehow converting that water into energy by some esoteric means, as discussed above. Strange how they didn't interfere with that, even after they were discovered. Could have caused the aliens a slightly bigger headache than they were already doing. Pre-denouement, at least.