I think it's fair to say that the most exciting teams to watch in the Champions League are Lyon, Barcelona and Chelsea (exept for yesterday). I don't know if you see the similarity between those 3 teams...
They all play 4-3-3 :

Chelsea

---------------------Drogba-----------------
-----Robben-----------------------J.Cole---
------Lampard----Makélélé----Essien------
-----------------------------------------------
--Del Horno---Terry--Carvalho---Gallas--

Lyon

-------------------Carew-------------------
----Malouda-------------------Govou------
------Juninho---M.Diarra----Tiago--------
----------------------------------------------
--Abidal----Caçapa---Cris----Reveillere--

Barcelona

---------------------Eto'o---------------
----Ronaldinho----------------Giuly----
-------Deco----v.Bommel---Xavi------
------------------------------------------
--Edmilson--Oleguer--Puyol--Belleti--

So what makes them the most exciting teams in Europe ?
Is it because of the 4-3-3 formation wich is itself exciting ?
or is it the team and the players ?

It's a combination of formation and players capable of working in that formation. I'm a fan of the 4-3-3 system. It's the system with the best field occupation allowing quick passing and fast attacks.
I'm not a fan of Chelsea though, I think they play the system to defensively. Although Lampard and Essien are quality players I still think it would be way more attractive to use playmakers on the sides of the midfield like Kaka, Van der Vaart, Ronaldinho etc.

Well, in the above teams, obviously 4-3-3 suits them. Attacking or not is another matter, it dpeneds on how you want to play. All teams rely on mentioned rely on the wings and most effectively, they have a very powerfull midfield

i also believe its a combination of good players and the formation. all three of these teams have both of these things.

and thanks for acknowledging that chelsea plays exciting football because they do but not many rival supporters will admit it.

EDIT: lol i just looked at your profile and you support all three of these teams

Yeah i dont know why people say they dont. They score a lot of goals and have some very skillful individuals in there team.

I don`t admit it, becose it is not true imo.
I see that Barca and Chelsea both are playing 4-3-3, but it is almost insulting if you say Barca and Chelsea styles are similar. Did you see what Barca did today? It is amazing how the ball moves and you just can enjoy every single minute of their play + players are individually so good it makes you just wonder if that is possible what they are doing on the pitch.
But Chelsea does maximum 2 short passes and then a long one to Drogba and maybe he scores or passes it to someone else and then this one shoots or whatever.
But really, you cant compaire Barca and Chelsea playing style...

Lyon on the other hand is playing very good football too imo. I belive they can go at least quarter finals when they play like that.

Chelsea are not an exciting team lol.

Boring, boring Chelski.

Arsenal, Barca, Real play the most entertaining football.

I don't think Chelsea play necessarily exciting football, but thats besides the point...

It's already been mentioned but I'll say it again. The reason the teams play these formations is because they all rely on wing play. It's not like any team can just switch to this formation and be exciting. This is just the one that is most condusive to the style of players they have... especially chelsea with Robben, Duff, SWP etc... All great wingers. While, in my opinion, they have a very average striker in Drogba. If they played a 4-4-2 they would not do as well because they could not use their great wingers and would rely on strikers. It's just a matter of suiting your system to your players... these teams have great wingers so they play 4-3-3.

Although I think Lyon and Barca play a bit different style from Chelsea, even though they have similar formations.

i didnt say that barcas and chelseas stles were similiar i mean i love watching Barcelona they are fu****g awesome i saw that match today 5-0 bloody mind-boggling great game lved every second barcelona are awesome and play lovely football but i still think chelsea's football is good to watch they score lots of goals as do barca and what is not exciting about that. Also lyon are an excellent team but are not similiar to chelsea.