Brilliant game, single player intense and worth it. Multiplayer phenomenal! My GOTY for 2008 without doubt!
I will start with the single player first. Well its an action packed ride with great graphics and non-repetative gameplay. The sniping sections in the Ukraine were particularly enjoyable for me. Along with the amazing SAS missions which i have never experieced quite the same feeling of actually being there! However the single player campaign is only about 10 hours long if played on highest difficulty. This is the downside, it is intense and thrilling but leaves you wanting more. This wanting more is not a problem if you like multi-player however :D......
Was addicted to the multi player from its release for a month or two just playing public and it was great. Getting all the achievements and challenges is very fulfilling. You get your 50th kill with a weapon and BAM you have a silencer for it. The feeling when you see that weapon all those other people have is finally unlocked is great. Obviouly some perks ala martidom (dropping a live grenade on death) annoy many people, but its all part of the fun! You call in airstrikes, UAVs and helicopters as you get kills which are all great/
The real thing for me was the great fun i had in clan matches with tactics and playing with others. Many perks dropped along with heli's uavs and AS, for matches best game for tactical fps clanning in my opinion.
In conclusion, the 10 hour single player is probably worth the money alone (only just) when compared to other fps (e.g. farcry 2).
The multiplayer on the other hand; wether it be casual or clan based can keep you hooked for 100s.
(this is obviously a PC review as i have not played it on consoles).