Looking for a relaxing Game

Bad Rats or Barbie Dreamhouse Party

Try some point & click adv games, like Machinarium, Botanicula, Samorost2 or Morphopolis

Or puzzle games, like Hexcells + plus + infinite

its not what you are asking but i play bejeweled 3 when i need to relax

Floating Point
(PS: It's free.)

Also adventure games will totally do it as Sewaz said... the thing is that this kind of game tend to not have almost none replay value so you would have to had a game per time you want to relax (being that most point and click adventure games arent long)

Super motherload
Pandora: First Contact

Stacking could be another good choice

Proteus.

To The Moon, A Bird Story, any of the Hexcells games, Windosill, Gone Home, 140, Antichamber, Audiosurf, Beatbuddy, Cosmic DJ....any of the BIT.TRIP games, especially the Runner ones

Not entirely sure if this counts but Brothers - A Tale of Two Sons. It's a nice game - I would recommend using a controller, but idk if it fits the "positive mood" 100%

I'd also say Dust: An Elysian Tail fits rather well :)

Edit: Not the best fits but kind of fit would be Portal 1 and Portal 2 if you haven't played them

grab your cup of cafe con leche and play Grow Home or.. drive around a spanish or hawaiian? island on Test Drive Unlimited 2

Braid, Eufloria, FEZ, Fractal, InFlux, Ittle Dew, Little Inferno, Night Sky, QUBE, Scribblenauts Unlimited.

Dark Souls.

Try something from here

Super Hexagon. You will love this game!

Here are a few things that I don't think have been mentioned yet. I have played all of them except for Proteus and Zen Bound 2.

Hero of the Kingdom
Lili: Child of Geos
Morphopolis
Proteus
Trine 1/ 2
Unmechanical
Zen Bound 2

FTL: Faster than Light

Pid. It was a freebie, it's a nice platform game, and it is one of those games with "cute" graphics and music and all that stuff. It has 3d graphics, but remember, it's a platform game, so you could say it has 2.5 graphics.

How about Life is Strange?

I seem to be recommending this to everyone lately, but... Homesick. The gameplay is similar to Gone Home. You explore an abandoned building and solve simple environmental puzzles. I think there's a horror element to it later on in the game, but what I've played so far has been very relaxing, despite the setting. The music is really beautiful and calming.

I love good humour! So I'll try to actually give some suggestions:

Prince of Persia (2008)
Xcom EU
L.A. Noire
Terraria
Zombie Driver HD
Legend of Grimrock
Call of Juarez Gunslinger

I know some of these might not seem like very relaxing, but that depends on what you think is relaxing. For me, for example, I would say COJ Gunslinger is very relaxing. I love western and the game has a pretty light and good mood to it.

if you are not playing in "Zen Bound 2" for beating record, it would be most relaxing game ever you seen

Mount&Blade : Warband , that game relaxes me every time.