I have a simple system.

Avoid like the plague.
Rent it!
Buy it nao!

That's why my scale is weighted honestly. You can see where everything is... and if need be i can list detail by detail what gained it points and what lost it points so it can be quantified. Sure it wouldn't neccesairly be standard... but everyone can see the work and decide what works and what doesn't.

It's a completely transparant system where you know what everything comes from.

Downside is it takes a long time.  

That and it's hard to figure out Genres sometimes.

For example I can't tell if Killer 7 is a shooter or an on rails shooter. On the one hand, you only move foward, on the otherhand.... you pick your movement.

Great game though. I don't know why everyone thinks the controls were so bad. The aiming can be a pain sometimes but i honestly think that enhances the game more then hurts it because of the "horror" aspects of it.

I don't think i've had more of a consistantly shocking expierence then suddenly realizing I missed an invisible cyberpunk suicide zombie bomber seconds before he lets off a Jokeresque laugh blowing up right in my characters face.

Ranges from:
>Never Play (Horsez)
>Play for laughs (Movie-based games)
>Play because of lack of something better to do (Gran Turismo)
>Buy Used (Halo 3)
>Buy New (Mario Kart Wii)
>Buy,Praise it in front of my friends every opportunity I get (World Ends With You)
>Transcendently awesome; I'm as amazed in future playthroughs of this type of game as I was the first time I played it (Final Fantasy 6)

Also in its own category would be "Steal-your-soul addictive, even though the game is rather simple and repetitive" i.e., Dr. Mario, Pokemon, etc

I don't really assign stars/scores; I just kind of give each game a mental ranking compared to other games I've played. 

1.0-1.9/10- avoid at all costs
2.0-2.9/10-terrible
3.0-3.9/10-bad
4.0-4.9/10-poor
5.0-5.9/10-average
6.0-6.9/10-above average
7.0-7.9/10-enjoyable but flawed
8.0-8.9/10-great
9.0-9.4/10-excellent
9.5-9.9/10-outstanding
10/10-virtually flawless

Pros and cons with each category briefly described as a section. Each section gets a 5-star/number system (Prefer star) A half is only used when a reviewer doesn't feel certain aspects are enough to destroy gameplay, but do detract from it (length of Battalion Wars).

Skip it- don't even bother looking at the game.

Try it- rent it or borrow from somebody.

Buy it- it's that good

and finally

Why are you talking to me and not playing this game- stop what you are doing and get this game now!!!!!!!

Did you overhear me using my review scoring system? Yours is identicle to mine.

Given that I am a subscriber to a rental service, it changes the way I choose which games to buy (longeivity becomes more important), I expect 10 hours out of a fully priced game apart from special circumstances

1-6 = ignore

7 = a game which has quite an interesting concept, and quite fun gameplay, but is not quite great and does get repetitive very qucikly (rent) (eg Folklore, Stranglehold)

8 = good gameplay etc, a bit more fleshed out then a game that just gets a 7, though still not fully developed in all ways and lacking in some form or another (rent) (eg Heavenly Sword)

9 = a very good game, that is nearly amazing, but just lacks the wow factor,and is fun to play (rent or buy) (eg. Burnout Paradise)

10 = amazing, not perfect, but incredibly fun, or just a brilliant experience, I am quite generous, and Uncharted, CoD 4 and GTA IV all make this boundary (definite buy)

I always like the 10 rating scale the most

0-5.9   Avoid, ignore, Imagine it doesn't exist, the lower the review score the more you'l regret

6- 6.9 Good enough for a rent or when theres a price cut/ passable

7-7.9  Good enough to buy but wont last that long/ won't interest all people

8-8.9 Very good game that you'll enjoy

9-9.9 Excellent game that you'll be glad you bought it

10 (rarely given) LEGENDARY! one of the best games ever

woot! 

A 1-3 star system.

1 - a game that I would not recommend anyone to buy. It could still be a decent game, but not good enough to validate a purchase.

2- A game that is worth buying, but it isn't top quality. Zack and Wiki, No more heroes and such fall in here.

3 - A great game. All the games in this category validate a purchase.

Simple as that, and if a game deserves more than 3, I'll simply state that in the text "this game is so good, there should perhaps have been a score above 3", but it still gets 3.