like the style of what you did there, bg changed perfectly. but for me, try to change small things, like just changing the wheels, lowered it and change the bg. it look mess, im sorry to said like this, cause the color is still toony, refs is bad, door lines too strong, fb off, window dont trough the bg. one more time, try simple thing first to make it realistic, but i like you courage to do it full brush, keep practicing bro !

I agree with SatwikaDe, but there are a lot of positives to be taken from this
->The rims fit really well, and look cool on this car
->The bg change has been done very nicely, and creates a very nice atmosphere
->The paint has the right tones and sort of general brightness to fit in with the backdrop

So it's not necessarily a bad chop
But there are some things you need to focus on:
->Reflections. Take your time, and really look at real cars and see how their reflections look. If you look at this diagram of a general type of reflection you should aim for to begin with, you will be able to see the difference:

As you can see, it is split into three main sections, light reflections from the sky, with clouds etc on them, then an almost solid line where much darker colour starts. This is reflecting a stretched version of everything you see below the horizon (skyline). At the bottom of this, there is usually a lighter reflection of the tarmac on the ground. What you will notice is that there are clear 'lines' between areas of colour, and these are what make it look shiny. If you try and add these into your paint you will see a big improvement

So to give you something to compare, I've done a very quick 30 second bit of messy brushing, to show you more the sort of reflections you want to aim for. Now remember, these aren't perfect, and aren't always right - what you must do, is compare them to a picture of a real car with similar lighting to the background, so see how the reflections should look, but as a general rule, they will be similar to this:

The more detail you put in, the better it will look! So take your time and keep trying! But remember - you don't have to brush everything Even the best don't

Hope this helps dude! Keep practising, and one day you will be a great brusher

tnk SatwikaDe , also you ATC... but ATC i have a request you can make a tutorial with a reflections . pls:)

See if this helps:
http://www.autemo.com/forums/?t=11270

It probably won't, because that's more about a possible brushing technique,
But maybe soon I will make a tutorial for reflections