Much like other "simple" rulesets (The Song of series for example) these have the capacity to become a bit stale. The key is good scenarios and maybe some flavoursome rules added between mates.
I totally agree, but I also believe that statement about scenarios applies to any set of rules, as 'line up and bash the crap out of each other' gets old very quickly, no matter how good the rule set might be. Almost all my WAB stuff these days is scenario-based, for example...
At least Lion rampant has a wider variety of scenarios, unlike Dux Bellorum which, though it has some, they are a little more limited...