As an employee, you're possibly better places than anyone to make the call on whether it's a worthwhile long term investment. Do they have financial/corporate presentations for the employees? Do you read the annual reports? That's a very good start. Are they expanding/contracting as a business? Which sectors of the business are doing well, which not so well? Where are the opportunities for the firm? How's the competition looking? Etc.
Many questions to ask, and you'll be able to supply many of those answers. With blue chip companies like GE, it's about being able to buy them at the right time really. They probably aren't going to be stellar growers- the share price now is lower than it was in 1998, for example. Huge companies often have decent dividend yields though. Depends what you're after, whether you want an income (dividends) or growth. Look at past performance, things like EPS (earnings per share) growth, share price relative to profits, what the debt to equity ratio looks like, all the key financial fundamentals.
One issue with engineering companies like GE is that they are R&D intensive, so it takes a lot of money, to make money if you see what I mean. Developing new jet engines for example, doesn't come cheap. Same can be said for Rolls Royce. So potentially, there are firms out there that will generate income a lot easier, because their products are simple and require little development expenditure (Tobacco for example, though I wouldn't invest in tobacco for ethical reasons but that's a totally different discussion).
The upshot is that aviation (I realise I'm focusing on one aspect of GE here) is a rapidly expanding market, particularly in the developing world. So the potential order base for engines is huge. Again though, you'd have to look at the competition- Rolls, Pratt and Whitney, Chinese/Russian manufacturers who can supply emerging markets cheaper, etc.
I'm going on a bit now but in short, there's a lot to consider, which is usually the case for investing. Shout up if you want any opinions or advice.