I am thinking about buying Shovel Knight. 
I am a big RPG fan and love games like Dark Souls. 

1. How is Shovel Knight?
2. Is it a 2D RPG?
3. Is it like Dark Souls in 2D?
4. Is it a difficult game?
5. Is it a long game?
6. Are the trophies difficult in this game? 

Thanks for everyone who can give me some information about the game!

I'd say its a solid yes on getting shovel knight. I've played a little on it, but I really enjoyed it. To answer your qs, I think it's best to say its a platformer, but a really great one with clever uses of the shovel, and since you'll get the vita version, you can fight kratos. That's cool, right? ; ) I dunno about the trophies, I got the wii version after all.

If you want to play Shovel Knight: Yes.
If you don't want to play Shovel Knight: No.

I can tell you one thing, this is NOT 2D Dark Souls.

With that said, if you're a fan of classic 2D NES games, like Mega Man, Castlevania, abd Duck Tales, you'll love this game.

1. How is Shovel Knight?  Its really good
2. Is it a 2D RPG?  No.  Its a 2D platformer
3. Is it like Dark Souls in 2D? It is very challenging yes.  It also has a similar money system, but no
4. Is it a difficult game? Yes it is challenging and i ike that
5. Is it a long game? Havent beat it yet but on average it takes 6 hours to beat http://howlongtobeat.com/
6. Are the trophies difficult in this game? Idk, i never pay attention to achievements/trophies unless i like the game so much i try to 100% them

I would def recommend it btw

haven't played it, but looking at some achievement/trophy tracking sites, they seem to be pretty difficult.

Great
No
No
Depends on how good you are at platformers. If you've beaten a Mega Man it should be easy but fun.
Depends on what you're going for. One playthrough starts off at around 5 hours, but once you beat it you can go for all of the in-game Achievements which should easily triple your playtime at the very least. The no death run, speed run, etc. Should all be fun challenges. I still haven't beaten NG+ a year later (got to the boss rush and stopped).

I thought about getting it too but I can see this becoming free for PS Plus and GwG down the road so i'll wait until then.

1. Awesome, Shovel Knight is a mix of some of the greatest games ever on Nintendo Systems. It´s something like Megaman + Ducktales + Castlevania + Super Mario Bros 3.

2. Yes it is, you go to towns, talk with people, increase you habilities, buy new stuff, etc .But outside the towns the game is an Action/platformer that reminds a lot to games like Megaman and Duck Tales, but with more exploration, more hidden secrets. The story is decent and the writing is very funny. 

3. Kind of, everytime you die you lose a lot of money, the money stays flying around the place of your death and you have to recover it. If you die before, all money is lost, and you need the money to buy new abilities and stuff even in the middle of the levels, so you want to have always money just in case. It´s painfull when you lose it.

4. Yes, the game it´s difficult. But the learning curve is good, it starts being accessible and it gets very hard with time, but is not as fustrating as a souls game can be, you learn in a more pleasant way, but you die a lot.

5. It´s surprisingly long for an indie game, it depends on your skills but the game is around 8 hours. With all the extras and the completionist stuff is around 12 hours. And it´s highly replayable. Plus on PC there´s a great free dlc called Plague of Shadows where you take control of a different character, its very game changer and it has it´s own story and new stuff, it´s coming to consoles too, don´t know when. Also on Sony systems you have to find and defeat Kratos :P. It´s a long game for it´s price.

6. I would say yes.

It´s one of the best games of the last year imo. One of the best retro-indie games ever made, it doesn´t just make you feel nostalgic about those great games on the 16bit era, it feels as funny as all of those games, but it doesn´t feel old, at all.

Very nice answer, thank you man!!!