How is the border crossing entering Bratislava from the Autobahn due east from Vienna?

Is there a marked difference that I would notice as I enter the eastern bloc?

Both countries are in Schengen, so there is no border in the formal, passport checking, sense. Bratislava is, on one recent measure, the most prosperous place in the whole former Eastern bloc and the only one not qualifying for any sort of EU financial support. As you get beyond Bratislava, it is simply more rural and less developed, the further east you go. It is very beautiful.