is this cassette and chain ring combination good in terms of number of teeth? I recently bought a used bike which has a shimano alivio 8 speed gearset. When I look at the drivetrain, it really looks small to me. Below are the size of them in terms of the number of teeth:

chainring: 24t,34t,42t

cassette: 11-23T.

Is this combo ok? From what I read this is not the standard no of teeth for chainring and cassette? Are their any drawbacks of using this combo?

EDIT

It's a hybrid bike (Specialized Sirrus) and has 700*32 wheels on it. As for my riding style I mainly ride it on the road, pavements and bicycle trails.
I read that as you already have a bike with this gearing, you're asking if its okay, not whether it will fit and work.

You might want to recount the teeth on the big ring.  42 is not impossible, but 44 would be more common based on the other two.

Assuming this is your 11-23, 11-12-13-15-17-19-21-23, and that you're on a 700 wheel with 23mm tyres, then Saint Sheldon says this at  http://www.sheldonbrown.com/gears/

Little Middle Big chainrings

4.2   5.9   7.3 (metres of forward roll per complete pedal revolution, 11 tooth)

3.8   5.4   6.7

3.3   4.6   5.7

2.9   4.1   5.0

2.5   3.6   4.4

2.2   3.1   3.8

1.9   2.7   3.3

1.6   2.3   2.9  (same, but for the 23 tooth gear)

So its a road bike with a granny gear for steep hill climbs.  The 42 chainring limits your top speed a little, and the 11 tooth rear will have mechanical loss of efficiency compared to a 12 or 13 tooth.

There is nothing wrong with your combination.  Use and learn what you want, and where you struggle. Personally I have a 25 in the rear and a 22 on the front, and I still struggle with steep 20% grades.

Once its a bit more worn and you know what you want, then replace the chain and cassette with a range to suit your riding needs.