Interesting idea; I think I'll go ahead and give each system my own score, too:
Xbox 360: B- Sales are down YOY, and most of its big games have been games that fall into the stereotypical category of games that are on the system. Adding this to plummetting support in Japan is only going to add to the problem of the stereotypical shooter-system. 2010's score will heavily weigh on Natal, and that's where part of the problem of this year is- most of the hype is for something slated for next year.
PS3: B+ Compared to last year, its sales are amazing. The price drop this year has also helped it immensely. Unfortunately, exclusives coming out this year are still not quite up to par as a whole, though this appears to be resolving next year. Not to mention the fact that the PS3 is still costing Sony money; if they can fix this problem, I'd feel more confident in Sony in general.
Wii: B Sales are still through the roof, and we're finally starting to see some games. However, like in the past, the largest franchises continue to get shafted entirely, or only see spin-offs. As things go on for the Wii, this trend seems to not be reversing. With more seemingly quality exclusives next year, I'd like to be proven wrong. But this still seems like poison to a few 3rd party companies.
PS2: D- It... still makes Sony money, but really, I can't think of anything worthwhile that came out on it this year in Japan or the US. New games for the system in stores is dwindling fast, as are its sales. Even a drop to $100 only created a small boost. If this were discontinued for game development entirely in 2010, I'd not be surprised. I see Sony trying to keep it around for the profit, but I think it'll be a tough sell to the retailers. Bigger box stores like Target, Wal-mart, Best Buy, etc, may drop the system entirely.
PC: ? As I'm not a PC gamer; it's not fair for me to try to judge this.
DS: A It's near perfect. It continues to break sales records, it has a slew of games, including exclusives, it gets decent support, all this, and it's what, 5 years old? However, I don't care for the fact that Nintendo is getting revision-happy on it. The DSiLL came out a little too quickly after the DSi for my taste. And while it's not come up yet, I'm not happy with the DSi adding in region-locking for DSi-specific games.
PSP: C+ New game releases for this outside of Japan really seems to be coming in spurts. We'll get a few good games, then nothing for a while, then a few more games. Like Nintendo and the DS, Sony is also revision-happy on this system, but at least the core system didn't get updated this year. It also seems as though game sales for this just can't get a break, and games continue to falter, as does seemingly, some 3rd party support. It's still the best competition Nintendo's had in portables since the Game Gear, though.
PSP Go: D- This is a different enough beast. Sales on it are poor, especially in Japan. (The past few weeks has seen the 360 and the DSLite outsell it about 3:1.) It's got a limited game selection compared to the PSP, and some of the games you have to pay more for. Add this in to the fact that there is no used market, and it just doesn't seem to be going anywhere. Sure it makes Sony money, but with sales this poor, I can see it being dropped by big-box store again... wait, I think I see where this is going...
iPhone: D Well, there's tons of apps. Literally. That's really its only strength. It costs the most of the handhelds, and there's a saying "Jack of all trades, master of none." It tries to do too much, and as a result, becomes a mediocre phone, a mediocre gaming device, a mediocre MP3 player, etc. Both DS and PSP control better and have a better selection of games. Sure, there's the occasional gem on the iPhone, but do you really want to wade through 1500 pieces of crap to find it?
