Microsoft has responded to the price hike for Halo 3: ODST that was revealed at last week’s E3, saying that the game is much more ambitious than previously envisioned, and now is more than just a Halo 3 expansion.

Shortly after Bungie’s latest first broke cover last year, there were claims that the game was not going to be a full price affair owing to the campaign’s three to five hour running time.

However, Halo 3: ODST is now being listed as a full-price game on several retailer’s sites. ’At the time of those statements, the overall scope of Halo 3: ODST was not yet finalized, and since then the project has grown increasingly more ambitious’ Microsoft told Joystiq in response to the swelling.

’We believe this standalone experience is much more than just an expansion,’ they continued, ’Halo 3: ODST provides a new campaign from the point of view of an entirely new character. Combine that with three new multiplayer maps, the entirely new cooperative mode called Firefight, and the complete Halo 3 multiplayer collection on a standalone disc, we feel this is a good value and tremendous addition to the Halo franchise.’

Our look at Halo 3: ODST’s campaign at last week’s E3 certainly suggested that the game will be worthy of its full-fat price-tag, though we’ll have to reserve final judgement for the game’s release this September.