Microsoft Active Directory isn't easy to setup either. Actually under Linux a simple no frills LDAP server is easier to setup and maintain than a full blown Microsoft Active Directory server. I speak from having managed it in an SMB and Enterprise environment. There are times I wanted to slap the designers and developers of AD for the choices they make and how unstable it could be at times.
There are a few good SMB Linux distros out there if you are wanting LDAP and SAMBA4/Active Directory setup. I would recommend looking at: ClearOS, Zentyal, NethServer and Univention. You can also get in to the whole Novell Directory Services (NDS) which is now owned by NetIQ and called eDirectory for hardcore directory services (X.500 Directory which includes DAP, which is a superset of LDAP). X.500 and the NDS are much better than Microsoft AD in my opinion but then Novell started doing directory services way before Microsoft. But I am starting to get way off topic here.