There is nothing wrong with Shimano 2300, do you realise that there are certain gears that you shouldn't use, this applies to any groupset whatever the cost?
All "20" speed systems only really have 18 useable gears, the gears that you should avoid, simply described are as follows,
1. The easiest gear on the casette (biggest cog) when using the outer (biggest) chainwheel at the front.
2. Now the opposite, the hardest gear on the cassette(smallest cog) when using the inner (smallest) chainwheel at the front.
These combinations don't work very well due to the extreme angle of the chain and should be avoided (crosschaining).