Awhile back I made this exact transition myself. I had been in a series of systems engineer and systems architect roles for the prior five years or so, and made the transition to sales engineering.
The people that thrive in technical sales tend to be folks that enjoy discussion directly with customers, can speak off-the-cuff about technical matters, and can look at a problem both from a big-picture standpoint and with a detail-oriented eye. You need to be prepared to socialize, to work with salespeople and their attendant quota pressure, and to help close deals while not violating your technical integrity. I actually think the Wikipedia article on Sales Engineering gives a nice description of the role.
Mike gave a great answer, but I thought it might be helpful to give you my own sort of "Joel Test". One thing I want to be clear about is that unlike the Joel Test, some of these bullet points don't have an inherently positive or negative answer. You may find yourself thriving in work environments of either style.
Do SEs carry a quota? - In our organization SEs have a "soft quota" individually from an overall performance standpoint, but our commission is paid based on the overall achievement of the group of sales folks we support, e.g. I along with a few other SEs support mid-market enterprise accounts in the western U.S. This format works well for me as it smooths out the hills and troughs of the compensation curve while still allowing me to affect my bottom line. Individual achievement is still recognized as well through other rewards.
When do SEs hand a solution off? - In some organizations SEs are deeply involved in the implementation phase of a solution, while in others there are separate folks and the interface is simply one of information transfer. Working the implementation phase can scratch a technical itch, but can also mire you in task switching from selling to support.
How do SEs share knowledge? - In an org with multiple SEs sharing solution designs and tips is critical. It keeps the customer experience consistent and saves you time reinventing the wheel. Our team uses an extensive internal wiki.
How well do the Product people work with the SEs? - Close alignment between Product and Technical Sales is key. SEs are some of the best-equipped people to tell the Product teams what customers need and want. Conversely, Technical Sales folks are dependent on the Product teams to provide well-documented products with attendant training, and should work with Product when coming up with qualification criteria, business cases, etc.
How technical are the salespeople? - You may work with a variety of skill levels on the sales side. Some reps may know the product inside and out and only need your help for esoteric one-offs or complex configurations, while others might require handholding to design even the most basic solution. You may prefer that the reps "stick to the numbers" and let you handle all the solutioning yourself, or you may prefer a more collaborative approach.
How much travel is required? - My company is fairly flexible with this. I travel out-of-state probably once a month on average, but it can be quite a bit more if I have several important meetings to attend. Your travel preferences will vary.
How is territory divided? - This ties heavily in to travel. If you prefer to travel to a particular area due to family, weather, etc, this could weigh heavily on your enjoyment of the position. It sounds like you are the only SE for now but if you continue in this career field you will probably work in a larger organization at some point.
What are the rules of engagement? - Quota-bearing sales folks often have complex rules of engagement in order to ensure that they don't step on each others' toes, e.g. if an opportunity comes from a referral by an existing customer, how does it split between the install base folks that serve that customer and the acquisition folks that might take the deal to fruition? Poorly planned ROE can result in a lot of friction between sales reps, and if you support multiple reps you don't want to be caught in the middle.
What's the after-hours culture like? - Some companies (or individual salespeople) have a significant wine-and-dine style of opportunity development. Usually these sorts of events are not required, but consistently being absent can negatively affect your political capital, and may also hurt your ability to sell to the customer. Attending can also mean a lot of tasty dinners on the company!
How are SEs seen by the company and their customers? - The SE straddles a fine line between helping the company through sales, but also helping the customer by being a trusted advisor. As the technical person in the mix you tend to be trusted more than the actual sales rep, but different organizations promote or suppress that divide in different ways.
Do SEs roll up to sales leaders or a separate leadership? This relates somewhat to the previous item. In some companies SEs sit alongside sales reps on the same teams, while in others the technical sales/solutioning organization is separate, at least at the middle management level. This can affect how your compensation works, your career prospects, the general culture, etc.
Does the company promote ongoing training for SEs? - This is more important in some companies than others, depending on the breadth of solutions they offer, but SEs must stay on top of technical trends and always be ready to speak to technical tangents the customer may head down. It's very important for companies to see SE knowledge as a key resource and promote constant upkeep of your capabilities.
From a personal standpoint I have been extremely happy with my move. I now get to focus on the big picture (but still go down to the nitty gritty), talk to a wide variety of customers, and have a direct impact on the company's bottom line day-to-day.
