I'll admit I'm sceptical about Valve adding unlockable weapons to a casual game such as Team Fortress 2 but the idea is definitely an interesting on. It worked, for example, in Battlefield 2 and 2142, but those games had a radically different play style, attracting a more, shall we say, dedicated gamer type on to the ranked servers on which killing and capture point taking added to your global standing and afforded you new, better, weapons. TF2, conversely, generally attracts a lot more casual players who are unlikely to appreciate being killed by more experienced players with better weaponry. Although, Valve is adamant that none of the upgrades will make the classes ‘better' but rather will simpy offer different gameplay styles.
The way you get to the new kit is fairly interesting though, as it will require the unlocking of a number of achievements, which do at least force a bit of teamwork. In case you don't know, these are the awards you get for meeting certain requirements, such as killing X number of enemies with your bone saw, or healing a bazillion points of damage and Valve is adding 35 new ones for the Medic, the first class to be offered the new unlockables.
The first new Medic weapon is a different healing ray which rather than adding an extra 50 per cent health to the target instead doubles it, but at the cost of either increasing Übercharge recharge time or possibly even omitting it altogether - Valve has yet to decide. The second weapon is also going to be a different healing ray but the specifics have yet to be decided. To unlock the two new weapons being made available you'll have to acquire either half or all of the class-specific achievements, no small feat.
In addition, there is also news that a new game mode is to be added to the game, along with new maps to accommodate it. The premise is simple: a mine cart has to be escorted by the Blue team to the Red base. The cart moves when Blue players are nearby and the more of these the faster it goes, however if a Red player gets close enough the cart will stop. Not much else is clear about this mode yet, but I personally think it sounds rather interesting and look forward to seeing how it, and the forthcoming unlockable items, pan out.