I believe that an agile approach is best for projects where the requirements are fuzzy and a lot of interaction is required to help shape the end user's ideas.
However… In my professional work, I keep ending up at companies where an "agile" approach is used as an excuse as to why no effort was put into an up front design; when the requirements are well understood.
I can't help but thinking that if the agile approach wasn't around, I'd be sitting here with a nice high-level specification and not having to revisit the same screen and functionality every second day when something else crops up or so and so hadn't thought of that.
Are the benefits of agile methodologies really enough to outweigh the excuse for being lame it gives to cowboy technical leads?
Update: Ironically I'm now a certified Scrum Master. One of the papers presented on the Scrum course observed that the best development process was one where there was a single expert or guru making the design decisions, however that has obvious weaknesses. Scrum shifts the responsibility for producing quality software to the "Team" which means a sub-standard team can get away with churning out spaghetti which I guess is no different to other Agile and non-Agile development processes.
Best Answer
I believe if you're using Agile development as an excuse for cowboy-style programming, then you're not really following Agile development. Cowboys will always be cowboys, no matter what process you give them.