The Finn was only able to complete 40 laps at Jerez on Thursday, after problems with his seating position and other minor electronic niggles restricted his time in the car.
Yet he said he had seen enough to be convinced about the step forward his team had taken.
"For sure it feels better than last year at this time," said Raikkonen, when asked by AUTOSPORT for his general feelings on the new Lotus.
"I think we have a good car, but how good it is this year we will only see it during the races and during the season. But it is not a bad start."
Team-mate Romain Grosjean had been positive about the good feeling from the car in all areas, but Raikkonen felt that he had not yet explored its full potential.
"The changes are not massive but it feels better for sure," he said. "We are missing some parts but there is no bad point on it. It is a normal first day.
"We did one change and used only the hard tyres.
"We still don't have all the parts that we will run in the races and we had last year, so it only can get better. It is not too bad."
Raikkonen says work undertaken on his seat position over Thursday, which included revising the location of his seatbelts, had improved matters considerably, and should allow him to get on with a full programme on the final day.
"We did some work on the seat, like is normal for the first test," he said.
"You make the seat at the factory and then it feels OK, but you can only tell when you drive. It is OK now for tomorrow and we can start the day properly."
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