Just a little perspective.
Yes Moyes has done badly, there is no excusing that - however;
1) Rio, Vidic and Evra should have been replaced years ago with experienced players, not waited for the last minute and bring in youngsters with little top level experience or a real budget buy like Buttner. Evans, Smalling and Jones are all individaully great for where they are in their careers, however they all need a real leader beside them to bring out the best (and the latter two have a ? over them in regards to injuries). I honestly dont think Moyes /the Club had any choice about when /how allowing Vidic / Evra to leave came out. Damned if the club release it themselves (mid-season) damned if they allow others to say they are signed for 2014/15.
2) We all know SAF was sprouting BS about "value in the market" in reference to midfielders 2 or 3 summers ago. Its been a gaping void really ever since Keane left. Carrick has done very well for himself for the most part, but he is the wrong type of player / cant do it all on his own.
3) Nani was a good gamble worth taking, but he has had at least one dodgy season even before Moyes arrived. I was hopeful of Young being a success, but unfortunately that never happened. Valencia had a great 1st season, got weighed down by being given No 7 last season, and hasnt recovered. Kagawa was never going to work out on the wing and now have an equally if not better No 10 in Mata (if Rooney is given the No 9 position next season). This is specificaly mentioned because GREAT wingers are in the heritage of the club.
These are all inherant problems with the squad some if not all SAF should have resolved before leaving (if anything else, SAF and Gill would have found it a lot easier to persuade players to join than an unknown in Ed Woodward, in regards to transfers, and an CL untested manager in Moyes).
Jan was always going to be tough to sign most players (in comparision to the Summer) due to cup-ties and the WC and players from abroad not wishing to acclimatise mid -season and risk WC places. Yes last summer was very disappointing but maybe the club should have tried harder not to let go of Gill and SAF in the same summer?
Moyes tactics have been awful at times (and the squad hasnt exactly given him that much choice at other times due to injuries etc) and some of what he comes out with could be a lot more inspiring - but then maybe this is because we are all far too used to SAF for the last few years?
Without knowing the exact scale of the job Moyes has taken over and having grown with it SAF possibly took for granted the only person who really knows is Mourinho from his time at RM (Im sure the scale of both jobs is probably similar, but maybe even this is wrong). Maybe even Pep has an idea from seeing the internal workings of both Barca and now Bayern.
Again maybe just because SAF dealt with everything for so many years doesnt mean Moyes should take everything over now (maybe he has, maybe he hasnt I havent seen anything to suggest one way or the other) and there maybe should be more delegation in the background (whether its for Moyes going forward, or who ever comes in next).
Remember 90% of the dressing room (a close approximation) was signed by SAF and a lot of senior players knew before Moyes arrived they werent going to be around for long, this is going to be a difficult situation to start with. Without Rio's idiotic tweets (no surprise there then) and the contract situation mentioned above.
Both of Moyes signings have barely played more than double digit amount of games due either to injury or arriving in Jan and being cup-tied for some games. Whether either were ideal Man Utd players is questionable, but at the very least Mata's quality is undeniable and should hopefully benefit the squad /1st team in the long run (and its heavily debatable whether the headline amount for MF is actually what Utd have paid to this point).
Given his lack of success however, I would think about a compromise for this summer. Raise ~£40m from the sale of RVP, Nani, Young, (Zaha?), Buttner, (Anderson?) and give Moyes £100m + (but no where near the £200m rumoured) to get two high profile players and 3 -4 budget players and see how things go upto December. Bring back Powell and promote some youngsters to the squad as well)
If Utd qualify for Europa (which I hope we dont) then I hope we send a junior squad to the first few knock out games