Having failed to find any kind of reviews online that would give me an idea about the changes between editions, I just bit the bullet and purchased the watermarked PDF of the 2.2 edition of Twilight: 2000 from drivethrurpg.
At first I was thinking that I just wasted 15 bucks... the changes seemed subtle and for the most part it duplicates the 2.0 book I own in softcover.
However I've been curious for over ten years now what changes they made in the 2.2 update, and as I delve deeper into this book, I like some of what I see.
They shifted the resolution mechanic from a D10 based resolution to D20.
Rather than doubling the skill ratings, they - as I expected - simply have you add the controlling attribute to the skill rating. (in 2.0 the only impact controlling attributes had was to affect the cost of raising skills - raising it over the attribute level cost double)
what I did *not* expect is that they shifted the difficulty rating scheme. So where equal to or rolling under your "asset" score was "Average" in 2.0, it is now "Difficult". This subtle change pleases me greatly.
The other big change I've found so far is that they've balanced the various "careers" a little better. Before, you could play a Green Beret who would have a ton more skills than a regular ground-pounder. Now, the Green Beret will have better initial training (to show for the more rigorous entry requirements for that career) but the playing field is levelled for long-term experience across all careers in terms of the number of skill points earned.
the other change that I was not sure about but think I like (in light of the shift in task difficulty) is that there are now diminishing returns for playing older characters. Now, your grizzled old Sergeant Major who fought in Korea, Vietnam, and both gulf wars will still (in addition to needing a hearing aid) have more skills than your fresh-faced recruit, but he will not have so many more as to make him a battlefield god.
Combine this with the fact that your veteran tanker with twelve years of service will, in fact, actually be more skilled than a navy SEAL fresh out of his first tour of duty, and you've got a system that looks to address some of my misgivings about the 2nd edition character generation system - namely the potential for vastly differing "power" levels.
[Not that I think differing power levels *have* to be a bad thing - look at the great story that happens when you put a 20th level wizard, a 15th level ranger, three 10th level fighters, and four 1st-level halfling rogues together for an adventure - but that requires extremely careful storytelling.]