For full emersion, the traditional baptismal font is cruciform, and in the floor (most of the surviving baptistries taht i am aware of are like this).
Also, there is ample ancient witness to and canons for what kind of water is to be used: “living water” as it is refered to in the Didache, The Apostolic Constitution, and On the Apostolic Tradition. This is taken to mean that flowing water is used, and such would be piped into the baptistry (an ancient baptistry in Corinth is right on the river).
That said, such baptismal fonts were not in the main part of the church structure itself, but in another room (in latter times) or in another building (such as the famous Arian Baptistry in Ravenna). So what i feel is probablamatic when i see these in new RC churches is not their presence per se, but two things: location and aesthetic (which are almost always bad anyway in newer places). Of course the ones with the constant waterfall are always a distraction when there is a service, and there is no barrier between the font and the nave.
In Christ,
Adam