I'm having trouble deciding on getting a Eurorail pass or just getting train tickets as I go.

I will be travelling to Europe in June for a month. I fly in and out of Dublin. My basic itinerary is to go straight to London when I land, then to Barcelona, Marseilles (or somewhere in South of France), Italy (Firenze..maybe Venice..not too sure yet), over to Croatia, Germany and finally back to Dublin. I'm having trouble deciding on getting the 10 day Global pass (~580) or getting train tickets when I'm there. I've heard good and bad things about doing either idea.

Does anyone have any insightful experiences that could help me decide?

Ultimately I do not want to be locked down to dates at each place so I do not want to buy them all in advanced even though that would probably be cheapest.

Thanks!