I spent the 3 years at IBM on a two-man team, which had periods of being a one-man team. I'm wasn't doing the work of 14 people, but otherwise it's a similar position to yours. I was a graduate hire, so this was very early on in my career.

It hasn't been all bad. I was able to leverage the work for a quick band promotion, some amazing resume statements, and met some exceptional senior developers. Something that I did find quite nice was that when you're the only developer, you're the senior/lead developer. It's very easy to become a specialist and reference for other teams or clients that use the product, which brings with it a level of job security.

But it's not all good. In return for the quick growth, I've become very narrowly focused on a single product and a single client. I haven't learned many new technologies, I haven't been able to dive into Agile, and I haven't been able to grown non-developer job roles. I've learned a narrow scope of version control and development cycles, so a lot of the other projects in the Professional Marketplace want experience in technology I've never had the need to touch. I quickly became 3 years out of date on new technology.

So I wouldn't say this is a "good" situation. It's an opportunity, but it's also a risk of career stagnation. I would strongly encourage you to move on after 6-12 months, or at least cut your hours back on this project and take on a second one. Riding out the full 3+ years is going to cause some career growth issues.

I guess it begs the question, how much experience do you have outside IBM? Were you a graduate hire like me, or are you coming here with 20 years of development experience?