Good question redcard
Pensions have had a bad rap recently, but overall, I think pensions are still valuable (see below). However, this will depend on your personal circumstances and your life-view (amongst other things), and there are also potential downsides as you say (also see below).
There are lots of things to consider, but generally I see pensions like this (these are generalisations and therefore not financial advice

)...
Main Pros:
- Getting money for nothing off employer (not to be sniffed at these days)
- Get tax relief on your contributions - so if you are a 20% tax payer, for every £8 you invest the government also add £2 - if you are a 40% tax payer then it's even better, for every £6 you invest the government invests another £4 (again, not to be sniffed at these days)
- If you live a longer than average after you have taken your pension then you "win" financially over the annuity provider
- Investment returns may be good over the next few years if we're currently in a recession (debateable, and it is usually the long-term forecast that you need to consider for pensions products)
- Growth in investments is tax-free (like ISAs) on most assets that pension funds invest in
- Can take upto 25% of the value of the fund as tax-free cash (currently upto a limit of around £375k !)
Main Cons:
- Lots of pensions rules means it's less easy to get your hands on your money (compared to say ISAs), e.g. you (usually) have to take at least 75% of the value of your pension as a regular income of your lifetime
- Investments can go down (as you say)
- When you buy an annuity at retirement, this can be costly, as insurance companies need to make a profit - it mainly depends on financial conditions and competition in the market at the time you buy, which is hard to forecast in the long-term
- If you die sooner than expected after retirement you will "lose" financially (although if you choose a 'spouse's pension' at retirement then that may be OK if spouse lives a long time)
Good luck pal and if in doubt get some professional financial advice