Maybe you've not been reading this thread very well, because so far the aliens are barely given half a chance. And just compensating with number isn't going to work, really.
Wait, are these the same aliens who know exactly where we are at all times?
In addition, unlike the alines that drop onto farms to kidnap yokels and mutilate cattle, these are going to be aliens who know they are going into heavy fire. They are expecting heavy resistance and so they should all be wearing medium or heavy armour. There are only a few weapons available to the player that will garauntee a reaction-fire kill of a heavily armoured alien, and most can be fired once or twice at the most, so if large waves of aliens in heavy armour come pouring around the corner the player is going to be screwed if he is relying on reaction fire - especially if the aliens make forced entry into two locations.
Most missions are painstaking games of hide-and-seek - and over a large area, that can get pretty tedious. I think that changing the pace for the base invasion missions would be a good thing, and add an air of desperation to the proceedings instead of the current miasma of drudgery.
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And I have been reading this thread right from the start, and fail to see where abouts the aliens not being given half a chance comes in. If you are talking about the shoot-downs prior to invasion, that's a concious choice by the player to dedicate resources to air defence. Again it would be readily defeatable in most cases - the fluff text talks about UFOs escorting each other, and if a harvester and 2 fighters come flying in as a group its going to be very hard for most players to shoot them all down before they arrive...
