With the absence of any Prince of Persia titles on Virtual Console, there's not really anything available for download in the way of acrobatic platformers in which the objective is to nimbly climb up ledges and perform almost pixel-perfect leaps. DSiWare's GO Series Tower of Deus somewhat fills this empty space, but mostly keeps things simple.
The basic structure is a bit like GO Series stablemate 10 Second Run. You're climbing up a big tower with 40 different stages inside, and you have to beat each one within a time limit. This time limit isn't actually displayed on screen, but it's represented by your health bar; apparently even being in the tower is bad for your health, so you'll constantly be losing life even if you're just standing still.
Not too far in you'll start encountering monsters and traps, which will also take off health if they touch you, so of course you should try as hard as you can to avoid them. Luckily there are also small and large health crystals that restore about a quarter and half of your health respectively, so stay on the lookout for them.
Early on, the game will throw new gameplay elements at you like there's no tomorrow, and you'll practically get a new one every single stage for about 10 stages total. After that things pretty much stay the same, and you'll only occasionally get some new gameplay elements which show up for about four stages after their introduction, after which they'll leave and never return, such as rising water and fire below you to keep you moving fast.
Your character doesn't really have many moves in his arsenal. He can basically only run and jump, as well as grab onto small blocks to pull himself up. He does actually have one special move, however, which you can use to get past any tight spots: hitting X at any time will make your character sprout wings, allowing him to fly anywhere he wants. However, this comes at the cost of your life bar draining about five times quicker, so don't make too much use of it. There are parts where it is actually required to fly, so if you get there without enough health, you might have to start over.
Despite all the new gameplay elements the game keeps introducing, unfortunately, things eventually start to repeat. Entire sections of stages are simply lifted from older ones and thrown into new ones with no change, so you will end up seeing certain block formations five or more times on your quest to the top with the exact same strategy to get past every single time.
The game's graphics are expectedly quite simple and they never really change, other than the level's colour palettes, which change every so often. It's not until the five final levels that you'll actually see some different-looking objects, but of course they still serve the same purpose. Those final levels are also the only ones with different music, as you'll be hearing the same tune over and over throughout the other 35. It's pretty catchy, but hearing it for that long is just a bit too much.
Once you've beaten the game, there's nothing really left to do other than improving your times. The game records your best record for every individual stage, so you can go back to any one you want and attempt to beat it, if you feel so inclined.
Tower of Deus clearly achieves what is pretty much expected of every GO Series title, offering a simple, fun, relatively short game experience. Unfortunately, there's not much replayability, and it may start to get repetitive after a little while, but for just 200 DSi Points, most people can probably overlook those issues.