The perceived problems with Merlin are cost (£32M each is often quoted), and a lack of robustness in the contemporary operating environment. True or not - open to debate!
Returning to the issue of Chinooks for a moment - "Medium Lift" refers to a capability, not necessarily to a particular size of SH. A loosely-defined capability perhaps, but traditionally we're talking about a helicopter capable of lifting somewhere between 12+12 and 20+20 troops. Given that we're likely to be operating in Afghanistan for much of the next decade, any Future Medium Lift helicopter would presumably need to be able to lift at least 12+12 in the prevalent hot-and-high conditions. That requirement rules out virtually all bar Merlin and Chinook. Notwithstanding the sterling work done by Merlins on TELIC, from a user perspective the preference for Chinook is clear and unambiguous. Hence more Chinooks should be part of the Future Medium Lift equation, whether they meet the general perception of medium SH or not.
That said, there is a definite need for a smaller SH type to perform smaller tasks in theatre; South Armagh-style tasking, for us old farts. I've no particular axe to grind regarding a preferred type, but I wouldn't dismiss AW149 out of hand. As a development of the widely-used AW139 it's a fairly low-risk programme, flying in 2009 with IOC in 2011. Further, AW149 is quoted as maintaining ISA performance in temperatures of ISA+35, whilst price is quoted at £15m each (versus £25m for NH-90). Whilst I take these figures with a huge pinch of salt, I would say that AW149 certainly merits consideration for the lower end of a "hi/lo" Future Medium Lift force mix - particularly given the political advantages of supporting AgustaWestland. It'll be quite interesting to see how AW149 gets on in the Turkish competition, versus Black Hawk...
Anyway, enough of my blah-ing; it's lunchtime!