Explanation of "Crisis"

Can someone explain the whole crisis thing? Was he more or less powerful after this event?

You really need to read it to fully understand it. It basicallly destroyed all but 5 of DC's universes and consolidated the remaining 5 into the current positive-matter DC universe.
It also erased all previous DC publications from continuity, and retconned the DCU to be as though the events previous publications had never existed.

Less powerful afterwards.

Before the "Crisis of the Infinite Earths" saga...Superman was uber powerful.

He could like sneeze and create a hurricane or fart and blow up the middle east. Pretty much waayyyy over the top. It seemed like every new comic Superman was topping his performance from the previous one.

The Crisis of the Infinite earth involves the destruction of the DC mulitverse. There were several different Earths, each in their own universe...the Anti-Monitor was the bad guy and he was responsible for the deaths of almost all of the multiverse....countless superheroes included.

Its easy
Before Crisis = nothing makes sense

After Crisis = it makes more sense

Basically they just started the whole Universe over, oh yes and Barry Allen died cry

Does barry exist at all post crisis?
I mean, is he still wally's uncle, or not???

yeah he is.

and was he ever the flash post crisis?

----------------

PRE-crisis:

+ve matter universes:
0
1
1a
2
2a
3
4
5
6
12
14
17
a
b
c
c-
d
e
k
s
t
x
crossover
fox
marble
mirror
omega
prime
quality
warren

(earths 1,2,4,x,s merged together in the netherverse to become the post crisis single earth)

-ve matter universe:
Antimatter Universe.

---------------------------

POST crisis:

+ve matter universes:
yahweh's creation

-ve matter universes:
Antimatter Universe

-----------------------

Post zero hour:

+ve matter universes:
Earth 0 (Yahweh's creation with alternate timelines via hypertime)
Lucifers Creation
Elaines Creation

-ve matter universes:
Antimatter Universe

-----------------

Yes Barry was still the flash, and the people somehow still remember the crisis but not that good you know.

Yeah. Lyla, pariah and lady quark still remember it at the end of crisis.
Rip Hunter still remembers it well. Waverider mentions in zero-hour that everytime rip hunter says the word 'crisis' that it feels strangely familiar, though he cant remember the event itself

Wally remembers that Barry died during a/the "crisis"

There has only ever been one antimatter universe (even when the positive matter multiverse existed).
However, it is ment to be about 60zillion light years across, compared to the positive matter universes each about (27 billion light years across).
So the antimatter universe is millions of times bigger than each of the +ve matter ones.

I thought most people in the DCU remember the CoIE as a big battle called "crisis" but they don't remember the details. Does Metron (of the New Gods) remember Pre-Crisis history like Rip does?

Not Sure.
People who remember it well include:
Harbringer
Lady Quark
Pariah
Alexander Luthor (not sure if he died in it or not)
Rip Hunter

Hmm who is Rip Hunter?

a good site for the crisis...

http://www.io.com/~woodward/chroma/crisis.html