I really think the main blame for the issues with the reputation of Solo encounters in 4e should be laid squarely in the lap of the MM1 chromatic dragons. They certainly CAN make good solid interesting opponents, but their design in and of itself doesn't particularly support or encourage that. You have to work at it. There are some other MM1 solos that are less than inspiring as well (the Purple Worm is certainly a flagrant example).
I find that the issues are really generally a good bit smaller than they are made out to be though. MM2 solo design tends to just internalize into the design of the monster some of what earlier solos need to gain from environmental factors. Nothing is wrong with that and it makes them more CONVENIENT monsters to use, but not always better.
Certainly when I put a White Dragon in a cave with a bunch of stalactites that could drop, several sheets of treacherous icy terrain, and gave it several Chillborn Zombies for allies it easily made a fine and interesting encounter. Maybe the last 2 rounds were starting to get a bit slow, but that kind of thing is easily solved as witness several suggestions above. Mine was simply to have the dragon change tactics and then bargain with the party when that didn't seem to help it. Overall it worked out very well in the context of the whole adventure and was an interesting fight.
I also wholeheartedly agree with the sentiment about not creating gimmicky styles of phases. Its a very heavy-handed DMing style to suddenly throw in some new rule just because the monster is below X hit points now and we have to create a different challenge. Its fine to make it part of the monster itself, that works out pretty naturally if its done reasonably. Doing it by simple "Now the monster flies and you have to fight the minions" is just video-gamey. Far better the purple worm example where the terrain evolves. Maybe best of all the black dragon example where the changes in tactics are sensible and fit the monster's personality and leverage its intelligent use of the environment.
I found the OP's version a bit heavy handed in the way his transitions worked where all of a sudden certain conditions and powers simply go away/don't work. In a video game you may not notice that so much and since the rules are not explicit it doesn't seem so jarring. In a 4e fight where the players KNOW the rules they will call you on that sort of thing. "Hey, my X power immobilized it, it can't just fly away." and players should always be able to trust that the rules are consistent at all times or if they are going to change in a specific situation it should be clear how, when, and why that situation comes up.