There are quite a lot....to think, understand... lets talk with few points
1 - Industry proven... maturity...stability
of course the open stack is great.. and it has great future...but still it is yet to prove...and accept. vmware is the pioneer.. they founded the perfect and complete recepie for the datacenter virtualization.. and now it is a perfect cloud OS and it is industry proven. and it is mature...
2- Management..
just leave the capability..or technical..details... at the end of day.. an organization is run and maintained by engineers...or admins..and not by the architects... so how easy to train a person.... how fast he can adopt the vmware... and how efficient is the management layer... the automation capablities...that matters a lot.
3- the hpervisor layer... or the virtualization layer
all the other vendors... like hyperv..citrix...kvm.. etc.. all need an OS assistance... the VMkernel is a highly evolved scheduler..which is ment and coded..and built for one JOB that is to run VM... so less number of CODE in the software.. and less bug
and less vulnerablity
4- Enterprise features
every one tells and claims they have all features...but how many of these features are proven and accepted and solid in the production environment...
the vmware features like DRS, HA,SDRS,SVMOTION, DPM, FT...memory reclaimation technique.. NIOC, SIOC... VAAI... VDAP... vDS etc... alot ..even a single DPM feauture will be enough to save money in the cooling and electricity cost.....and to show it is worth to invest in VMware... but how many of the other vendor have these and proved... these vmware features are not just features...they are True inovation and cutting edge technology....
5- journey to cloud..
every body says they are in to cloud... and they are capable.. I am surpised...others they didnt even achieved maturity and proved in the industry..in the VIRTUALIZATION layer then how come they can claim...they are in to cloud.
6- Support
This is the key... who is accountable... or responsible...or who will take the ownership if some issue happened in the critical production...?
in the Opensource..no body will take... that part, the solutions may work or may not... it will be a super solution or it may screw your system.. so its a TRIAL AND ERROR and LUCK...if there is a bug in the code who will correct? will you wait for X days or hours until some one give some free solution in the internet...for the critical system...? in here you will loose the business...for enterprise they have SLA and they will solve.
7- Business continuity & disaster recovery
What will happend if my enitre SITE went down? how fast i can bring my services...? ..is it possible to create an ACTIVE/ACTIVE sites...that is both sites are primary. ...the answer to these are VMware SRM.....
.. it just need FEW MOUSE CLICKS...!!
To run a busines... these are very critical...else you will loose the business...
SO what is there in open stack...and if any thing is there ... then how FAST it can...RTO can be acheived? ---- you wont get a perfect answer for this.
now to the openstack.... it is a great software..but who will customize....it..and who will give support..train...and how will you manage..monitor...will it give the features like the one which vmware gives...?..how fast you can adopt..into your IT...? and lot of questions still there to ask and you will get almost zero answer...
these software and solutions can be managed and modified....by the GIANTS like GOOGLE... facebook.... Rackspace...etc.they have the manpower...time ..capital... etc....but for others... it is not possible..
now all these openstack..opennebula...KVM....it is free........super...lot of savings... AT the end of DAY who is responsible if I loose the BUSINESS ?
But VMware is costly...it is true...so who cares..? If i want to win a F1 race i need Ferari car.. and with a FORD or FIAT normal car.. you cant win. the RACE. Here COST is not the issue...and no body cares...Here what matters is... What technology...how stable it is...with that CAN I win a RACE...?
There are lot of technical... and other comparisons...in depth..these are just my thoughts...and I am not BIASED ....also. As of now...in terms of COST others can beat VMware...and every body says this also.. But interms of Technology...they are the LAST WORD.