Saw Whiterabbit's comments about reported install impact on the GOTD game page etc., so in case this helps...
TO start with A Sirius Game requires .NET 4, Direct X 9.0C Feb 2010, & Microsoft XNA Framework 4 -- if you don't have those it won't run, & will ask to install them for you during install. A Sirius Game also has graphics hardware requirements -- the game's site only says DX 10 hardware, but one error message said I needed Pixel shader 2. In testing it also failed to run in a win7 SP1 32 VM, with Event Viewer showing undefined .NET errors related to graphics hardware, so if it won't run for you it might take a bit of digging to find out why. If you meet [or are willing to meet] the software installation requirements, you *might* want to try bypassing the .msi installer routine, using Universal Extractor [http://legroom.net/software/uniextract] to get the "A Sirius Game" program folder you can then just cut/paste into Program Files or Program Files (x86) -- I didn't see any game specific registry entries etc. added to the registry, nor special files added to the User folders, but bear in mind I also couldn't run the game in the VMs where I could monitor this stuff, so I can't say I got the game working without a full install.
RE: .NET 4 -- not a huge deal in Vista/win7, but potentially a Very big headache in XP, where I've had more than the expected amount of problems with it. IMHO don't add .NET 4 to XP unless you really need it, & be prepared for for a bit of a slog as you add not just .NET 4 but any/all updates to it. As always back up 1st, & also be prepared for a lot of changes to Windows plus [if I remember correctly] a gig or so of added files/folders.
RE: DX -- AFAIK most people have it, & thankfully A Sirius Game doesn't insist on running the web installer to verify... My regular XP Pro install has had it's DX installer messed up, so the DX install won't run -- my research indicates that's not all that uncommon.
RE: XNA -- I recorded 60 files added & 380 registry entries added, so it's not that bad. I've not had any issues from having XNA installed since beta.
As for the game itself, it uses the Windows Installer, which I personally detest because it doesn't check for or prevent the coder(s) using it from doing very stupid things. With the game's Microsoft software requirements using an .msi setup file does make sense, but I can't say the same for this dev's implementation of it. 1) IMHO there's little or no reason to copy a 110 MB msi file into C:\Windows\Installer. 2) Since as far as I can tell the game itself doesn't use or rely on anything stored in the registry, 2496 registry entries added is to me a bit insane. Now msi files do add a lot of registry entries all by their lonesome, but [as Whiterabbit noted] this is the very 1st time I've seen an msi file add an entry for every one of the 1107 files added. Hence, if installation impact on Windows bothers you, I'd suggest giving the Universal Extractor route a try -- the GOTD setup file is basically a WinRAR self extractor that gives you "A-Sirius-Game.msi", use UniExtract on that to get A-Sirius-Game\PFiles\A Sirius Game, & cut/paste that last "A Sirius Game" folder into Program Files, or Program Files (x86) if you're in 64 bit Windows. Then run "A Sirius Game.exe", as admin if in Vista/7, & if it works create your shortcuts.