Ignoring the .NET version problem, not using LINQ probably makes plenty of sense, given that implementing a LINQ solution would be much much more complicated to

Ignoring the .NET version problem, not using LINQ probably makes plenty of sense, given that implementing a LINQ solution would be much much more complicated to implement than what you've done. Breaking apart expressions to get to your XML requests would be hard. I also think the proposal above where each criteria is expressed as an individual lamdba is the worst of both worlds in terms of ease of implementation and readability.